The Last Oak Tree ( TV story ) The Last Oak Tree was the fourteenth episode of series 1 of " K9 " . Synopsis . Panic ensues when a museum exhibit is stolen . K9 , Starkey , Darius and Jorjie are on the trail of the culprit . They find a giant menace hiding in London ' s abandoned sewer s . Is the alien the threat or is Drake the real evil ? Starkey and K9 face annihilation as they try to rescue the alien ' s hatchlings before a bomb destroys them all . Plot . In a museum , K9 , Jorjie and Starkey stroll through a virtual reality Sherwood Forest . They find a notice stating , " Here stood the Major Oak , sanctuary to the outlaw Robin Hood and his band of Merry Men . " Jorjie tells Starkey she thought she would marry Robin Hood when she was a kid . When Starkey notes that both Robin Hood and the Major Oak are long gone now , a virtual reality simulation of Robin Hood comes out of the trees and contradicts him . He says the Major Oak lives in the museum and welcomes them to Sherwood Forest . K9 says he should be shorter . Robin is shocked at this " sorcery . " Jorjie is surprised K9 has met the real Robin Hood . When Starkey asks Robin Hood about his tights , he tells him it was " chilly " in his day . K9 confirms that Britain was three degrees cooler in the Middle Ages ; Robin notes that pollution has affected the planet and the oaks and silver birches have been cut down or died out . Robin Hood starts to glitch and loop and K9 detects an alien threat . They turn off the virtual reality forest as the patrons flee . A Department officer says a signal of alien origin is causing magnetic interference in Sector SE14 Delta . They patch into a CCPC ' s vision and June sees the CCPCs malfunctioning . She orders Inspector Drake to the scene . The curator insists the oak tree hasn ' t been misplaced . K9 detects an unidentified alien species and decides to investigate . The Major Oak has been stolen . June arrives and stops the CCPCs , who think the curator is a suspect , with a command override . They find a hard , alien substance where the tree used to be . K9 scans it . It could be vomit or snot , but he needs to examine a sample . He blasts off a chunk . Starkey picks it up and they run off . At the mansion , Gryffen listens to news of the theft . K9 , Starkey and Jorjie arrive to show him the alien substance , which K9 says is emitting a high - pitched frequency . As June examines where the Major Oak was displayed , Drake arrives with orders from Lomax . The aliens have been classed as an A - level threat , " which means it ' s time to let the big boys play " . June claims this is not his jurisdiction , but Drake picks up a piece of the alien substance . Gryffen tests the substance ' s magnetic field , confirming it made the CCPCs malfunction . K9 is not affected . Unlike the CCPCs , his electromagnetic shielding is impenetrable . Darius arrives , wondering if the museum is offering a reward , disgusting Jorjie with his selfishness . Gryffen asks Darius if the post office had his invitation for the Annual Bournedecker Awards for Scientific Excellence . When Starkey wonders if he ' ll leave the house , he says he won ' t . Gryffen says that he sees it as a tradition that every year he gets an invitation and every year he doesn ' t show up . Darius suggests the postman lost it . In fact , the postman is trapped underground by the alien substance . Gryffen completes the analysis of the substance , which is actually paper - mache . Whatever they ' re dealing with is genetically altered . When Starkey wonders why it chose the Major Oak , Gryffen states that many species target one species . Considering what it did to recycled paper , he hates to think what it could do with the Oak . K9 suggests that he return to the scene of the crime and scan for a trail . Jorjie says the museum is probably patrolled by the Department , but Starkey says they know where to find the thieves : in the sewers . K9 , Starkey , Jorjie and Darius search the sewers . Gryffen detects interference while monitoring K9 , and asks him if he ' s all right . K9 replies that it was just a spike in the electromagnetic interference . He finds oak leaves on the floor . June contacts Gryffen to tell him the alien substance has stumped the Department scientists . Gryffen says they ' re " slow - witted " and he has already unravelled the sample ' s mysteries . Gryffen says that the thieves won ' t make ransom demands as they aren ' t looking for trade and already have what they came for . The team finds slime on the sewer walls . Darius , Jorjie and K9 move on . As Starkey takes a closer look , he finds slimy oak leaves , hears a creature growling and decides to move on . Gryffen monitors K9 , who seems to be confused . K9 confirms he is experiencing the same electromagnetic interference created by the substance from the museum and stares into space . K9 tells Darius the interference is getting worse . Darius looks around and finds no sign of Starkey . As Starkey searches , his light flickers and he calls out for his friends . The creature ' s growls grow louder as the light dims . When it turns off , the alien creeps behind Starkey . Darius and Jorjie hear something fall . The creature drags Starkey to its lair . Jorjie asks if K9 is sure he knows where he ' s going . He tells her that he does . Gryffen ' s videolink with K9 starts to break up , but K9 tells him everything is all right on his end . Gryffen knows something is affecting K9 ' s circuits . He compares the high - pitched frequency of the alien substance to a dog whistle . It is sending out a distress signal . He tries to tell K9 but communications are scrambled . Starkey , now trapped in the alien substance , warns the alien what Jorjie will do once she finds out what they ' ve done to the Major Oak . The postman is trapped next to Starkey and hopes that Jorjie is a " super soldier with a couple of bazooka s " . He gives his name as Patrick . Starkey gets his dog whistle out and calls for K9 , but this only gains the attention of the alien creature . The magnetic interference weakens and Gryffen can talk to K9 again . K9 notes that the magnetic interference matches the pitch of a dog whistle . Gryffen explains to Darius that K9 was confused as he ' s been following an alien distress signal . K9 will consider the alien hostile until he can confirm Starkey is safe . As Starkey whistles again , Patrick and he are released and fall to the ground , where they sees alien eggs . Starkey continues to whistle as K9 races to find him . K9 , Jorjie and Darius find Starkey , but before K9 can neutralise the creature , Starkey shows him the eggs ; the creature is a mother , and its lair is a hatchery . The creature doesn ' t want to attack or eat anyone . She ' s just protecting her babies . Gryffen tells K9 not attack the creature , known as a Centuripede . She ' s here to build a pod for eggs , or as K9 and Darius put it , an " interstellar baby carriage " or " a spaceship made out of wood and centipede spit " . She specifically needs oak wood . Centuripedes have bred in oak forests for thousands of years , but since there are no more oak trees this may be the last spawning of the Centuripede on Earth . June contacts Gryffen , who reports the situation to her . She says that both the alien and K9 are " history " if Drake catches them . Drake sets a gas bomb to detonate in four minutes . Darius runs with Patrick , who is carrying Jorjie , who doesn ' t want to leave the aliens . K9 insists that Starkey leaves , but he wants to help save the aliens . K9 tries to keep the gas out with a photon spread , but he can ' t guarantee he can give the creature enough time . Starkey decides to " make time " . As K9 holds off the vapour , Starkey helps the Centuripede put the eggs in the pod . As the others make their way out , K9 ' s power depletes . As the others climb up the ladder , K9 uses his maximum power . Darius is the last to climb up , rummaging through Patrick ' s postbag to find Gryffen ' s invitation . As Jorjie , Darius and Patrick get out of the sewer , they see no sign of Starkey or K9 . K9 can ' t hold his power much longer , but Starkey places the final egg and the pod rises . The mother collapses and appears to be dead . K9 ' s power is exhausted . Starkey goes to the mother , whose body cracks into white light , knocking him down . The mother transforms into a butterfly - like creature . The bomb explodes . Darius says there is no chance they could have survived . They spot the mother and her babies flying up into their pod . Darius and Jorjie believe Starkey and K9 dead , but Starkey , who is with K9 behind the others , says how beautiful it was . Starkey tells them the creatures gave them a lift . Starkey shows Jorjie a " token of appreciation " from the creatures : three acorn s stashed in their nest from Robin Hood ' s time . Darius shows Gryffen his invitation on his monitor and discusses his finder ' s fee . Patrick protests that Darius can ' t charge people for their mail , but Darius snatches the envelope and runs away while Starkey and Jorjie laugh . The Department ' s propaganda messages reappear in the sky . Story notes . Ratings . " to be added " Myths . " to be added " Filming locations . " to be added " Production errors . " to be added " Home video releases . This episode is featured in the following DVD sets :