Battlefield ( TV story ) Battlefield was the first story in season twenty - six of " Doctor Who " , which would ultimately be the last season of the original 1963 - 89 run of the series . Nicholas Courtney made his first appearance as Brigadier Lethbridge - Stewart since 1983 ' s " The Five Doctors " , and Bessie appeared for the first time since that serial as well . Following Courtney ' s death in 2011 , this serial marked his last televised performance as Lethbridge - Stewart in the series proper ; that same year , his character was written out of the series in " The Wedding of River Song " out of respect for the actor ' s passing . However , Lethbridge - Stewart as a character would return to the series approximately three years later , making a cameo in Cyberman form near the end of " Death in Heaven " in a brief scene paying tribute to the late Courtney . This was also the first story to feature UNIT since " The Seeds of Doom " ( bar a brief appearance in " The Five Doctors " ) and also the last of the classic series — UNIT would be featured once again in " Aliens of London " in 2005 . Jean Marsh , who played Sara Kingdom in the 1960s , returned in this story in a different role . The Seventh Doctor ' s costume was also modified as of this story : to coincide with his darkening personality , he replaced his French grey jacket and red - banded hat with dark brown equivalents . Interestingly , " Battlefield " introduced the idea that the Doctor was the man behind the myth of the wizard Merlin at some point in his life . Since this ended up being one of the final stories of the classic series , the full details behind this mysterious plot line were never worked out on television and instead interpreted differently across the " Doctor Who " expanded universe as multiple writers tried their hand at explaining these untold events . Synopsis . The TARDIS materialises in the English countryside near the village of Carbury , where a nuclear missile convoy under the command of UNIT Brigadier Winifred Bambera has run into difficulties . Lying on the bed of nearby Lake Vortigern is a spaceship from another dimension containing the body of King Arthur , supposedly held in suspended animation , and his sword Excalibur . Ancelyn , a knight from the other dimension , arrives on Earth to aid the King but is followed by his rival Mordred and the latter ' s mother , a powerful sorceress named Morgaine . They all recognise the Doctor as Merlin , which the Time Lord attributes to events in his own future . A battle breaks out between UNIT and Morgaine ' s army . Brigadier Lethbridge - Stewart has come out of retirement to assist in the crisis and ends up using silver bullets to kill the Destroyer — an awesomely powerful creature unshackled by Morgaine to devour the world — although he himself is almost killed in the process . Morgaine tries to fire the nuclear missile but is overcome by shock when the Doctor tells her what nuclear war would really mean , and that Arthur is in fact dead . She and her son are then taken prisoner by UNIT . Plot . Part 1 . Brigadier Lethbridge - Stewart , now retire d from teaching ( TV : " Mawdryn Undead " ) as well as UNIT , is enjoying retirement with his wife Doris . UNIT may still need the gallant old soldier , though ; new Brigadier Winifred Bambera and her soldiers , in a nuclear missile convoy near rural Carbury , are faced with inexplicable equipment failure and peculiar sightings of armour - clad knights . In the excitement , the UNIT convoy ignores a pair of hitchhikers nearby : the Seventh Doctor and Ace , lured to Carbury by a distress signal so powerful that it even crosses universes . The Doctor and Ace eventually hitch a ride with archaeologist Peter Warmsly , who is excavating an old battlefield near Carbury — though even he is surprised to find his dig site taken over by tight - lipped UNIT soldiers . While he attempts to get an explanation , the Doctor unearths old UNIT identification ( his own and Liz Shaw ' s ) to get himself and Ace into the UNIT camp . Bambera , nonplussed , confiscates the passes and ejects the two travellers from the convoy . But one UNIT soldier , who had previously served under Lethbridge - Stewart , recalls UNIT ' s former scientific advisor : his eccentricity , his ability to change appearance , and his tendency to attract trouble . Intrigued , Bambera gives the Doctor and Ace a lift to the nearby Gore Crow Hotel . . . and asks UNIT headquarters to recall Lethbridge - Stewart to duty . At the hotel , Ace meets a kindred spirit in Shou Yuing , while the Doctor talks to innkeeper Elizabeth Rowlinson . She is blind but psychic , and knows that the ancient scabbard over the inn ' s fireplace — an artefact found by Warmsly — is an object of tremendous and mysterious power . Ace and Shou are chatting outside the hotel when they and the Doctor witness an oddly human - shaped missile crash into innkeeper Pat Rowlinson ' s microbrewery . It is revealed to be a knight in full armour — not an android , as Ace initially thinks — and , when his helmet is removed , he warmly greets the Doctor as " Merlin " . Part 2 . The Seventh Doctor , Ace , and Shou chat with the knight , Ancelyn , who refers to the distress signal intercepted by the TARDIS as " Excalibur ' s call " and claims that it heralds the start of a final war and King Arthur ' s restoration to the throne . The Doctor surmises that the coming battle isn ' t properly part of this dimension at all , and belongs to a parallel universe — but before he can test the theory , an exasperated Brigadier Bambera storms into the microbrewery and declares everyone under arrest . She is interrupted by the unexpected arrival of more extradimensional knights , including Ancelyn ' s sworn enemy Mordred , who " also " recognises the Doctor as Merlin . After Mordred retreats , unwilling to face the Doctor , Ancelyn and Bambera vie for dominance and the rest of the party retreats to the Gore Crow ' s lounge . Mordred , with the help of a sword he calls " brother to Excalibur " , begins a strange ritual intended to link his home dimension to present - day Carbury and allow his mother Morgaine to cross over . As he roars in triumph at the ritual ' s success , the scabbard on the wall of the Gore Crow ' s lounge breaks free and sails across the room — towards the lake — before implanting itself in a wall , distressingly close to Warmsly . The Doctor realises what is happening , but cannot stop it . . . Morgaine crosses over , and the hotel is plunged into darkness . Morgaine and Mordred discuss their plans for battle ; the sorceress , seeing a helicopter approach , demonstrates her power by bringing it down . The helicopter , which is bringing Lethbridge - Stewart to Carbury , manages to land , and Lethbridge - Stewart sets off in search of the Doctor . Warmsly shows the Doctor and Ace the Carbury dig , and points out a mysterious inscription . The Doctor recognises his own handwriting instructing him to dig a hole , which he asks Ace to do with some well - placed explosives . At the bottom is an 8th century tunnel . . . made of cement . The Doctor and Ace investigate , having left Warmsly to guard them . At the end of the tunnel is a strange room . Ace and the Doctor look in vain for some way out , until the Doctor simply commands the door to open , and it obeys . As they proceed to the next rooms , the Doctor explains that Merlin must have built the rooms — spaceship , it now appears — that they are in . . . and he " is " Merlin , or will be . In the topmost level of the spaceship is King Arthur , apparently in suspended animation , and Excalibur . Ace accidentally draws Excalibur , which triggers an automated defence system that traps her in an airtight chamber rapidly filling with water , and renders the Doctor helpless as she begins to drown . . . Part 3 . As the two wander near Lake Vortigern , Warmsly quotes Malory ' s " Morte d ' Arthur " to Ancelyn . . . when , to his astonishment , a hand appears from the lake brandishing Excalibur . It proves to be Ace , whom the Doctor managed to free from the spaceship below the lake . She emerges wet but none the worse for the wear , and is joined by Warmsly , Ancelyn , Bambera , and , arriving with Shou in her car , which he has commandeered , Lethbridge - Stewart . The Doctor continues to fight the spaceship ' s defence system , but it is only stopped when Lethbridge - Stewart , who has entered through the tunnel , intervenes . Reunited , the friends leave by the tunnel and rejoin the others at the dig . Meanwhile , Morgaine has sent Mordred and his knights after the Doctor and the others , with orders to take Excalibur and kill any who resist . The Rowlinsons are terrified by Morgaine ' s cavalier killing of Flight Lieutenant Lavel , but grateful — if bewildered — when she restores Elizabeth ' s sight . The party splits up for the ride back to the hotel : Bambera and Ancelyn in Shou ' s car ; the Doctor , Ace , Shou , and Warmsly in his . Mordred ' s knights set up an ambush in the woods between the hotel and the dig , but ultimately attack the wrong car ; the others make it back to the hotel safely , with Excalibur . There they find that all locals are being evacuated — Shou and Ace slip away unnoticed , while Warmsly and the Rowlinsons protest but ultimately agree to evacuate . A UNIT patrol sent to find Bambera and Ancelyn reports that the two soldiers escaped the knights and are at large in the woods . The news , though welcome , does not entirely cheer the Doctor , who points out that Mordred and his knights are also at large . . . and that nothing stands between them and the now - unguarded missile convoy by the lake . They must return to the convoy immediately . Fortunately for the Doctor , Lethbridge - Stewart thought to bring along transportation : Bessie , the Doctor ' s car from his UNIT days . He and the Doctor depart , leaving Ace and Shou behind with Excalibur and instructions on avoiding Morgaine ' s sorcery . Morgaine leaps at her chance to snatch Excalibur from the hands of its young guardians , summoning the Destroyer to help her , but Ace remembers the Doctor ' s warning and draws a protective circle of chalk . Much to her surprise , it seems to work . . . until Morgaine tries a more subtle psychological attack , and sets Ace and Shou fighting , trying to draw one or both out of the circle . At the dig , the ancient battlefield has become a modern one , as UNIT troops face off against Mordred and his knights , and Mordred himself is confronted by Ancelyn — but as they prepare to fight , the Doctor intervenes and declares that there will be no more bloodshed . But Mordred smugly announces that the battle was only a diversion for his mother Morgaine ' s attempt at Excalibur . . . and that Ace and Shou stand no chance against Morgaine and the Destroyer . Part 4 . Mordred offers the Doctor a trade — the girls ' lives for Excalibur — but the Doctor , outraged , threatens to decapitate him unless Morgaine surrenders herself . But Mordred calls the Doctor ' s bluff ; he knows , he says , of Merlin ' s distaste for taking life . He is proved right , but Lethbridge - Stewart appears out of the woods , gun ready , and declares that he has no such compunctions . The two old friends force Mordred into their car and head back to the Gore Crow Hotel . They arrive just as the Destroyer , under Morgaine ' s command , has nearly brought the hotel down on Ace and Shou . The Doctor finds his friends under a pile of rubble , relieved that they were able to stay alive , even at the cost of surrendering Excalibur to Morgaine . She , meanwhile , has returned , with Excalibur and Mordred , to her castle in her reality . The Doctor and the Brigadier follows her across the void ; he himself is followed by Ace , who brings along Excalibur ' s sheath and the Brigadier ' s silver bullets . Morgaine frees the Destroyer , to the Doctor ' s dismay . While she and Mordred teleport away , out of the Destroyer ' s immediate path , the Doctor and his two friends are left to flee on foot . The Doctor deduce s that , since the Destroyer was bound in silver chains , it will be vulnerable to the Brigadier ' s silver bullets . Lethbridge - Stewart distracts the Doctor , knocks him out and takes the gun — loaded with the silver bullets — to spare the Doctor the duty of killing the Destroyer . When the Doctor revives , he and Ace find that Lethbridge - Stewart has done so , nearly paying for the opportunity with his life . Even without the Destroyer , Morgain and Mordred still pose a threat , as they prove when they cross back into our world and take Bambera hostage . They force her to divulge the launch codes for the nuclear missile , and prepare it for launch . Ancelyn , the Doctor , Lethbridge - Stewart , and Ace return Excalibur to the spaceship under the lake . There they find that the sword activates the spaceship — but does not resurrect Arthur . According to a note left by the Doctor for himself , Arthur was killed in the Battle of Camlann , not placed in suspended animation . The note also warns them that Morgaine has control of the nuclear missile , and the four friends rush back to the surface . While Ace and the Brigadier destroy the spaceship , the Doctor tries to stop the missile launch . Morgaine is obstinate . . . but the Doctor explains the full horror of nuclear warfare , and she relents with seconds to spare . She demands of the Doctor that King Arthur face her for a final confrontation , but the Doctor reveals that Arthur died in his last battle . Grief - stricken , she does not notice the Doctor leave . The Doctor intervenes in a sword fight between Ancelyn and Mordred , and renders Mordred unconscious . Ancelyn is freed , and Mordred and Morgaine surrendered to UNIT . Back at the Lethbridge - Stewart house , the Brigadier and Ancelyn are left to work in the garden while the Doctor cooks supper . In the meantime , Doris , Shou , Ace , and Bambera have commandeered Bessie for a girls ' trip out on the town . Story notes . Ratings . " Note : " This story received " Doctor Who " s lowest ratings in its history , with only 3 . 1 million viewers for part one . DVD , VHS and audio releases . DVD release . This story was released in Region 2 on 29 December 2008 . A two - disc set , it featured the original televised version and an movie - format version with new special effects .