The action takes place on Petrie's Island, off the east coast of Ireland--isolated, with a small village peopled with farmers and fishermen, with one constable, a "head" whose job is quite informal, and one doctor. Dr. Lawrence Phillips (Peter Forbes-Robertson) comes to the island and sets up a sophisticated laboratory, the most wonderous thing of its kind the islanders have ever seen, in a isolated mansion on the island's peninsula. Dr. Phillips and his number-one assistant Carson (Richard Bidlake) supervise the unloading of what turns out to be the last of their equipment. Watching from nearby, Peter Argyle (James Caffrey), the keeper of the general store, chats with Roger Campbell (Niall McGinnis), the "head" or mayor of the island; Constable John Harris (Sam Kydd); Dr. Reginald Landers (Eddie Byrne); and Ian Bellows (Liam Gaffney), an ordinary farmer. The most remarkable thing about Dr. Phillips is that he is a recluse. Dr. Landers explains that away by saying that all researchers close themselves off from contact from any human beings except their own teams and staffs. Ian and John remark to Mr. Campbell about all the promises that "the mainland" has made to the islanders, but never kept, because the tax revenues from the island are so little.In the laboratory, Dr. Phillips tells Carson that they will begin, without co-ordinating with their Rome, New York, and Tokyo teams. Phillips questions Carson quite closely on the state of their equipment. Finally he announces to his team that he will proceed with a revolutionary process that, he is absolutely sure, will yield the dream of the medical sciences: a successful and unfailing treatment for cancer.With that, he turns to. Then as the screen turns blood-red, the sound of breaking glass breaks out--as if to suggest a dangerous...something...breaching containment. A sequence no more than a frame or two long--a subliminal cut--shows Dr. Phillips and his two assistants lying dead on the laboratory floor, and the breached containment vessel. And then the main title begins.The action resumes, presumably that evening. The fog that Peter Argyle confidently predicted ("If you weren't a newcomer, you'd feel it in your bones."), has rolled in. Ian Bellows, carrying a lantern, reconnoiters a cave on his land near the Phillips house. Suddenly he hears an odd-sounding noise, mostly in the base register, and sounding like nothing so much as a kind of atonal music, weak on melody but strong on deep, pulsing rhythm with haunting sussurations. He walks into the cave--and then gives out a loud outcry. It is the last sound he utters. The next sound that comes from that cave is a sound very much like the one a child makes as he rudely slurps up the last dregs of a thickshake through a straw.His wife (Joyce Hemson) waits impatiently for Ian to come home. When he does not, she goes to Harris' house to complain and express her concern. Harris goes to the cave to investigate. He finds Bellows, or what's left of him--soft, flabby, face caved in, eyes and tongue bulging out. At once he fetches Dr. Landers, who asks Harris to help him take the unfortunate Bellows to the island clinic. There he performs a complete autopsy, that reveals little. Yes, it is Bellows, for apart from his clothes, Landers recognizes an old appendectomy scar that he, Dr. Landers, gave Bellows once. But Bellows' entire skeleton is simply missing.Landers first calls on Dr. Phillips, but no one answers the door. So Landers takes the emergency launch to the mainland, where he then gets more conventional transport to London. There he seeks out Dr. Brian Stanley (Peter Cushing), the most eminent pathologist in all the British Isles. Stanley admits that a case of a man with no bones has him stumped. He suggests they seek out Dr. David West (Edward Judd), orthopedic surgeon and the most eminent specialist in management of diseases of the bone.Dr. West is at this moment entertaining a flighty young lady, Toni Merrill (Carole Gray). She recently became his patient after she smashed up her Maserati and landed in the emergency suite while he, West, was the attending-on-call. After her discharge, West had her up to his flat for dinner--where he managed to spill wine on her dress. (Whether that was his fault or hers, the story never makes clear.) So when we first see Toni, she is wearing one of David West's shirts, and nothing else, and flirting outrageously with him. The truth of the matter is that Toni Merrill is the type one will find in all of Western civilization: a spoiled rich girl. And she has set her sights on West, primarily because she finds him dashingly attractive.In the middle of this flirtatious session, West's doorbell rings. West tells Toni where she can find his dressing gown, and then answers the door to admit Stanley and Landers. Toni, not shy in the least, comes out, and does not mind being the center of attention. She listens as Landers and Stanley explain their problem to West. The problem fascinates West, who would very much like to see Bellows' body for himself. The three men decide they ought to fly back, but how? Then Toni offers to prevail on her father to lend them his helicopter--on condition they take her with them on what she is sure to be a marvelous adventure. West is reluctant, but Stanley and Landers point out that time is of the essence. So West accepts her bargain.The four prepare to fly to the island, but their pilot tells them they can't expect him to wait, because Toni's father has need of the helicopter. So they will be effectively marooned. In the conversation that follows, they speak of solitaire, and Toni says she has a more interesting game in mind. Let the viewer interpret that however (s)he likes.The four fly to the island, and Constable Harris and a hunter named Dunley (Roger Heathcote) greet them.The first thing Landers does is take Stanley and West to the clinic and show them Bellows' body--which Stanley pronounces "not a pretty sight." The three perform more thorough tests, which yield a strange finding: micro-punctures, or micro-ruptures, all over the skin. As if something, or someone, injected something into the body--or sucked it out. They cannot tell which.Finding the clinic facility woefully inadequate to the task of conducting a proper autopsy, the three men then set out for the mansion of the reclusive Dr. Phillips. (Landers takes time to write a note to Constable Harris that he may find him there should he need to speak to him.) There they find Dr. Phillips' butler, his two assistants, and Phillips himself, all nastily dead, and all showing the same horrific disfigurement as Bellows. Stanley concludes: Phillips managed to concoct something in his laboratory that got loose, killed him and his team and butler, and then killed Bellows. And might kill any number of other people.To find out what, Stanley and West gather up all of Dr. Phillips' notes, to take them to the inn to study at greater leisure. But while they are doing this, Farmer Morton (Shay Gorman) discovers one of his horses dead, soft, and flabby. He reports this to Harris, who then sets out, on the strength of the note, to find Dr. Landers and speak to him. So Harris goes to Phillips' house alone, and finds pretty much the same things Stanley, West, and Landers have already found. And then, as he goes into the cellar, he now hears, for the first time, that strange, ominous, atonal, rhythmic and sussurating music. He follows it into the room that once housed test animals--and there a tentacle, with suckers on it like those on an octopus, snags him under his chin and causes him to cry out in pain. It is his last cry.The next morning, Landers goes to call on Harris but does not find him. Landers then goes to the general store, where he finds Peter and Morton. Morton informs Landers of his dead horse, and that he had told Harris about it. Landers notes that this happened on "the other side of the island," then rushes off--abruptly enough that Morton and Peter wonder about "strange goings-on." Peter decides to go see Mr. Campbell; this is something the Head of the island ought to know about.Campbell is not pleased at this news. He takes Peter with him to talk to some other farmers, see what they might have seen, and then go see Dr. Landers.Landers returns to the inn and gathers up Stanley, West, and now Toni Merrill, who insists on coming along. They stop by the farm to investigate the dead horse. Toni stays in the motorcar--and hears the strange music, and then, through the rear window, sees a horrible-looking mass of suckers slide past! She shrieks. The men come running and take her account, which doesn't amount to much, except that what she saw frightened her very badly.The four drive to the Phillips house, where this time they agree to take Toni with them--they now deal with a hazard that they can best defend against if they all stay together. Once inside, they descend into the cellar, where they find Harris--dead and flabby, like all the rest. And there, for the first time, they all hear the music that Toni heard, and then see what can only be the creature, or creatures, that Dr. Phillips created.Each creature is two meters across and flat to the ground. It looks like a turtle that moves on a base of suckers instead of conventional legs. It has a single tentacle that comes out of the front of its armor-plated dorsum and seems to act as combination sensor and prehensile manipulator. The four retreat from it, only to find a second such creature moving in from another corridor. Cornered by this obviously coordinated attack, the three back against a wall that happens to house the fire-fighting equipment. Dr. Landers takes down the fire ax and takes a swing at the creature in front of them. Not a scratch. He pulls back to take another swing, when the creature snags his ankle with its tentacle. Landers cries out in pain, again and again, and falls prone across the creature--and then, before everyone' horrified eyes, turns soft and flabby. Toni can't take it; she buries her face in West's chest and clings to him tightly.Now the creatures move in for the kill--and then stop. And then they divide, looking very much the way cells caught in mitotic anaphase do under a microscope--except that these creatures are two meters across! Happily, they go inert during this process, and that gives Stanley, West and Toni time to escape--though Toni is so badly frightened that West has to drag her along. The three rush from the house, only to see another of those creatures prowling about in the yard. They pile into their car--which won't start. West pops the hood and barely manages to fix the problem, close the hood, jump back into the car, start the engine, and drive off before that creature can overtake them.Back at the inn, West gives Toni a mild sedative and apologizes to her for bringing her to the island and exposing her to the hazard. She in turn apologizes for being so much trouble.Meanwhile, Campbell and Peter Argyle return to the general store. There they meet Dunley, who wants to know about an order of guns he had placed. Peter asks Dunley whether he has seen Dr. Landers--apparently he and Campbell haven't found him. Dunley says that Landers "left" at 7:00 in the morning, with three strangers--two men and a girl. Strangers who landed on the island by helicopter the night before. This is the first time Campbell has heard of three strangers on his island, all working with Dr. Landers, and now he is irritated. Taking Peter with him, they set out for the inn, where they might find all the strangers.West and Stanley return to studying Phillips' notes, when Campbell and Argyle walk in. The two doctors bravely admit that Dr. Landers is dead, and so is Constable Harris (and Ian Bellows), and that the island, its entire populace included, are in serious danger. Campbell reluctantly agrees to summon all the inhabitants to the village meeting hall, which adjoins the clinic.Campbell assembles everyone, as West and Stanley have suggested. Then Stanley and West, having finished studying the Phillips notes, address the villagers. Their story is dire: Phillips, in trying to create a culture of artificial killer cells that could attack cancer in a patient's body, instead created a creature of an entirely different order: one based on silicon rather than carbon, to which Stanley gives the name "Silicate." These creatures dine on animal and human bone. They inject a powerful enzyme cocktail into the body to liquefy the skeleton, and then suck this out of the body, using the suckers on their tentacles and ventral surfaces. The first such creature broke containment, killed Phillips and his team and staff, and then killed Bellows. And worse yet: these silicates reproduce by fission (which is what Stanley, West, and Toni witnessed) every six hours. There are sixty-four silicates on the island at present--and at six o'clock that evening there will be 128, and at midnight 256, and in three days there'll be a million of them (this after twenty fission cycles total, including the six that have already taken place; we may assume that Phillips and company died shortly before midnight the day before yesterday, and Bellows soon thereafter).West proposes the obvious: "deny them food." He suggests all the villagers camp out in the meeting hall and prepare for a siege. Then Campbell recruits a ten-member militia to try to attack the first wave of the silicates now approaching the village from the direction of the Phillips house. Morton, Dunley, and Halsey (Keith Bell) are among them. Reluctantly Toni Merrill stays behind--and ironically she finds herself in charge of keeping the villagers organized and, more importantly still, busy.Campbell sends Dunley to take two other men and scout three specific spots on the northern shore of the island. The rest of the island militia, with Stanley and West to accompany them, meet the wave of silicates, using long guns, Molotov cocktails (called "petrol bombs"), and finally dynamite. Morton dies when he gets too close, and all their measures prove futile.But then Dunley rushes up to inform them that he has found one of the silicates--dead!--and Dr. Phillips' pet Great Dane, half-eaten. Stanley and West drive to the site, with Dunley to guide them. They confirm that they have a dead silicate, loaded with radioactive material, and also the Phillips dog, just as radioactive. (Phillips had written in his log that his dog had gotten an overdose of Strontium-90, a radionuclide that bones would take up.) They drive back to the clinic and meeting hall, where West informs the populace that they might have a means to kill the silicates, but will need the help of everyone present. He then instructs Toni to keep the people busy, while he and Stanley examine their specimen. The dorsal armor is impenetrable, of course, but they are acutely sensitive to radiation poisoning. West then proposes that he and Stanley return to the Phillips house and lab to collect a supply of Strontium-90 and a pressure gun for injecting large animals with. They instruct Campbell to gather the villagers' cattle in his cattle yard to keep them away from the silicates, until they have time to inject them all with strontium. (They then say that if West and Stanley fail in their mission, Campbell and Argyle will have to get the strontium. Peter protests his ignorance, but Campbell tells him not to borrow trouble.)The mission to recover the strontium and the injector succeeds--but West must use the fallen fire ax to cut off Stanley's left hand when a silicate attacks him as they make their escape. West barely manages to apply a tourniquet and then get Stanley back to the clinic. There West, now indisputably in command, operates on Stanley (here Toni assists him as his scrub nurse) and prepares to inject the cattle. He manages to inject them all--except that he must cut the dose of strontium for the last several steers so that he does not run out.Campbell has a problem of his own: Halsey. He has the face to propose, and to an old woman (Margaret Lacey) yet, that they swim for it. Campbell tells Halsey to shut his mouth, assures the people that waiting inside the building is the safest course, and then takes Halsey aside. Speaking as sternly as he knows how, he tells Halsey that if he says one more word, he, Campbell, will knock him out and toss him outside to the silicates.At 2330 hours Irish time, the silicates gorge themselves on the cattle. And then they "mitose" for the last cycle. About 200 silicates (probably 224, accounting for one of them dying after the third fission cycle) then attack the building.The lights, over-strained when Campbell and his men strung several lights at the cattle yard, now fail. Toni rushes in breathlessly to ask David what happened to the lights; David tells her that they need to set an example of calm. Halsey panics, says he is "not staying here," and makes for the door--only to meet Peter Argyle, long gun in hand, blocking his way. Campbell does more than that: he fires a gun into the air to get everyone's attention, and instructs everyone to move away from the windows and doors.Three silicates break in through a side window, wrap their tentacles around Halsey, and kill him. Another silicate slithers up the wall, then across the roof, and then onto a skylight, which it then crashes through, killing Dunley beneath it. Campbell now orders everyone out of the room and into the clinic--and must slam the door on an unknown number of villagers when the choice is either them or all the rest! Hastily they barricade themselves in the clinic, only to wait for the silicates, their music now including a high treble cry, to start battering their way in. Toni Merrill, now reduced to a quivering mass of flesh, takes comfort in Stanley's right arm, while West prepares a fatal dose of morphine to use on her to spare her a horrible death. He is just about to ram the needle home when Campbell calls out that the silicates seem to be weakening.Sure enough, that dreadful music is diminishing in volume, loses the triumphal treble quality, and finally falls silent, as the last of the tentacles flop to the floor beyond the door. West waits fifteen seconds, then asks some men to take down the barricade. Setting his teeth, he flings wide the doors, only to see silicate after silicate lying on the corridor floor, dead. He announces his find, and Toni rushes into his arms.The next morning, Mr. Merrill's helicopter comes back to take them off. West promises Campbell that he will send a large crew to clean up the island and bury the dead. (Peter Argyle confirms to Stanley that he and his remaining friends searched the island and found not a single living silicate.) Toni Merrill is obviously a bit wiser for her wear. West tells her not to scare herself all over again, and then observes that they were lucky this happened on an island, otherwise they might never have been able to destroy these creatures.But evidently they have forgotten, for the moment, the part of Phillips' notes where he mentions that similar teams are working in Rome, New York City, and Tokyo. And in the very last scene, a scientist in the Tokyo lab hears the eerie pulsating and sussurating music, goes into his lab to investigate, and cries out in horror as he dies the same kind of death we have already seen....
Output: Question: What kills Constable Harris?, Answer: Offscreen tentacled creature