Colditz ( audio story ) Publisher ' s summary . October 1944 . As World War Two draws towards its conclusion , a Nazi defeat begins to seem almost inevitable . But that might be about to change . . . Two intruders are captured in the grounds of Colditz Castle , the most secure Prisoner of War camp in Germany . At first , the guards think they ' re dealing with British spies . But the strangers arrived in an advanced travelling machine , the like of which they ' ve never seen before . With this " TARDIS " in their hands , the Third Reich might triumph after all . . . Plot . Part 1 . An anomaly in the Time Vortex forces the TARDIS to land on twentieth - century Earth , but it ’ s unclear where exactly . The Seventh Doctor and Ace find themselves in an oddly familiar castle courtyard . The Doctor realises where they are , but too late ; they are apprehended by German soldiers , led by one Feldewebel Kurtz , and the Doctor is shot in the shoulder . They have arrived at the Nazi prison camp known as Oflag 4 - C — Colditz Castle . Now they are prisoners , and the TARDIS is in the hands of the third Reich . The camp brings out the other prisoners to watch Ace and the Doctor being taken in , under the watchful eyes of an officer , Hauptmann Julius Schäfer , and his prisoner friend Bill Gower . Ace gives Kurtz her real name , but refuses to show him any respect ; the prisoners are impressed by Ace . Kurtz finds the explosives and supplies in her backpack , and takes it as further evidence that they are there to rescue prisoners ; he is confounded by her CD player , but he takes it and her other possessions for study for the war effort . He sends Ace for delousing . Elsewhere , Schafer takes the Doctor into his custody , and warns him that he won ’ t be able to get proper medical care until morning . He also warns the Doctor that the camp commandant has taken an interest in the TARDIS after watching it materialise . The Doctor accepts the warning , but gets Schafer to promise to care for Ace . Kurtz arrives to report on Ace ’ s “ amazing technology ” , but is displeased to see Schafer caring for the Doctor . Schafer exposes Kurtz ’ s real issue : the lack of respect from the newcomers . He refuses to let Kurtz force Ace to strip naked for delousing . In retaliation , Kurtz keeps the “ technology ” secret , and returns to question Ace . Ace tries unsuccessfully to escape ; he takes it as an attack , but opts not to shoot her , instead informing her that she owes him a favour now . In the morning , as the prisoners report for roll call , the Doctor presents Schafer with the bullet , which worked its way out of his wound . Schafer sends him to the camp physician anyway , and warns him that the German High Command already knows about the TARDIS , and is sending a Gestapo soldier to torture its secrets out of the Doctor . The Doctor makes Schafer feel his double heartbeat , shocking the man badly ; but Schafer insists on waiting for orders . Meanwhile , Ace joins the other prisoners for roll call , meals , and recreation , and meets Bill Gower , who assumes she is a valuable prisoner on a secret mission ; he introduces her to another " prominenter " , or valuable prisoner , Timothy Wilkins . Ace mentions her escape attempt , and Gower explains that this prison exists specifically to hold prisoners who have already escaped elsewhere . No one has escaped for over a year . Kurtz goes to question the Doctor , but what becomes obvious is that he is being kept in the dark by his fellow officers . This feeds the man ’ s paranoia that he is unimportant . The Doctor plays on this fear and calls him a coward to provoke him , and Kurtz beats him . He is interrupted by the arrival of a woman named Klein , who takes charge of the Doctor and sends Kurtz to bring Ace . She knows the police box is a TARDIS , and demands the Doctor ’ s key , threatening to shoot Ace if he doesn ’ t surrender it . Part 2 . Tim Wilkins meets with Ace . He believes that Gower is withholding the truth — that escape plans are being made , but they only include those they favour . He intends to escape before the Nazis , who are being pushed back by the Allies , begin using the " prominenter " as bargaining chips . She is picked up by Kurtz , who takes her to the Doctor ’ s cell ; the Doctor is trying to probe at Klein and find out how she knows what the TARDIS is . She knows there is no record of their existence in this year , therefore she ignores his questions , and orders Kurtz to shoot Ace . The Doctor surrenders the TARDIS key . Klein takes him to meet Schafer at the TARDIS ; she orders Kurtz to kill Ace if the Doctor doesn ’ t cooperate . The Doctor tells Ace to work on Kurtz ’ s paranoia . At the TARDIS , he opens it for Klein and Schafer ; overwhelmed , Schafer refuses to do any more , and leaves to make a report . Klein admits that she isn ’ t here for the TARDIS , but for the Doctor . Meanwhile , Ace starts to mock Kurtz , who has dismantled the CD player ; she says that Klein will take credit for his work . He finds it hard to restrain himself , but manages it , and takes her to mealtime , where she sits with Wilkins . Gower joins them , and talks with Ace , who lets slip that the war will be over by next year . This persuades him to take her into his confidence . Tim cautiously agrees to create a distraction , allowing Gower to take Ace to view the prison ’ s weaknesses . Kurtz catches them in the kitchens , and strikes Ace , threatening to take out the favour she owes him . Ace shoves him , and he takes this as an assault , and drags her to solitary confinement . Klein returns the Doctor to his cell under the pretence of waiting for his transfer papers ; but he has picked her pocket , and obtained the real transfer papers , so he knows she is lying . He also obtained her identity papers , and knows they are forged ; she is impersonating the Reich ’ s representative , who has yet to arrive . He destroys the papers , horrifying her , until her reveals that they were blank ; he still has the real papers . He gives her the real papers , and orders her to hurry up , thus subtly establishing his power over the situation . She gets the Commandant to release the Doctor to her , in exchange for the TARDIS ; on the way out of the castle , they pass Ace en route to solitary , and the Doctor assures Ace that he will be back . Ace ’ s situation , meanwhile , angers the captive British officers , who — via Gower — ask Schafer for help . He can ’ t directly countermand Kurtz , but he is able to get Ace released from solitary , though she is placed on a punishment detail . Ace learns that there is no official record of the Doctor or Klein existing . Fearing what the Doctor may give up for her sake , she goes to Wilkins and agrees to help him escape … if they go tonight instead of waiting . Meanwhile , Klein takes the Doctor into the forest , where she has another form of transport waiting … but an indentation in the ground reveals the truth . Her transportation is the Doctor ’ s TARDIS — coming from some point in the future — and it is missing . Part 3 . Klein now intends to take the version of the TARDIS that is in the castle . As the Doctor and Klein return to Colditz , he pieces the truth together . The TARDIS is lost to the Germans in this year , 1944 , and retained by the Nazis until 1965 , the year from which Klein hails . In that year , she finds its flight logs and figures out how to get it back to its last landing point , at which she uses it to travel here . She intended to capture the Doctor and force him to explain the workings of the machine . He insists that she has actually created a causal loop — that is , by taking his key , she caused the TARDIS to be lost to the Germans in the first place — and now she will make the paradox worse if she takes the earlier version of the TARDIS , preventing it from ever being in 1965 . She doesn ’ t care ; she insists she can correct it later , and that her companions in the Reich in 1965 can interrogate him for the necessary secrets . With Tim Wilkins , Ace gets into the castle ’ s medical bay , where he has nearly sawed through the bars on the window . It ’ s the beginning of a plan , but needs more work to escape the guarded courtyard beyond . Gower catches them , and explains that this is why he won ’ t incorporate Wilkins into any plans ; the man didn ’ t even set a lookout on the sickbay , indicating he doesn ’ t have what it takes to properly escape . Still , Ace insists she only needs to escape temporarily , to take away Klein ’ s leverage over the Doctor and allow him to outwit Klein . Gower agrees to help , even if it means taking Wilkins ; Wilkins and Ace must fake food poisoning after the evening meal , so that they will be sent to the sickbay . However , before she can brief Wilkins on the plan , Kurtz arrives and sends Wilkins out so that he can deal with Ace . She is forced to claim food poisoning early ; Kurtz allows her a small victory in seeing another officer regarding the poisoning , but assures her he will have his chance eventually . Klein ’ s admission about the Reich in 1965 has cued the Doctor in to a problem . Klein , it seems , is from an alternate future , in which the Reich won the war , a future precipitated by his arrival here at Colditz . She isn ’ t actually German , just of German descent ; she was born in Britain , but welcomed the Nazis , and was fortunate enough to have Aryan features and hair and a Germanic surname . She argues with him about the validity of her timeline , and about his own refusal to change certain aspects of history . She refuses to give him anything to work with , but does tell him that history records that Ace dies tonight in a botched escape attempt , betrayed by a co - conspirator . Having heard enough , he slips his cuffs and captures Klein , shackling her to a tree , and leaving the handcuff key in sight but out of reach . He returns to Colditz . Gower threatens Schafer to get him to remove the guard from the sickbay that night . However , it ’ s for nothing , as Wilkins betrays the group to Kurtz , in exchange for being removed from the list of " prominenter " prisoners . Kurtz questions Schafer about removing the guard , but is unsatisfied by Schafer ’ s excuses , and watches the sickbay himself . Meanwhile , Gower puts on a fake German uniform , and insists on knocking out the sentry outside the window , but Ace insists on taking the risk instead , as Gower has more to lose . Tim is set to watch the second sentry , out of view of the window , and take him out when it ’ s clear . Later , Schafer meets Klein returning alone , and tells her that the Doctor was arrested in Leipzig while trying to steal a car , and will be returned in the morning . At the same time , the ill - fated escape is beginning . Tim back out , and Kurtz arrives and intercepts Gower and Ace at the fence . He sends Gower to solitary , but prepares to shoot Ace . Part 4 . Ace name - drops Klein to stop Kurtz from shooting ; killing her in direct defiance of Klein ’ s orders would destroy his career . He is angry , but returns Ace to solitary confinement . In the morning , when the Doctor arrives and learns of Ace ’ s survival , he knows that Klein ’ s future is changing ; it may already have changed enough to eliminate her timeline . Klein decides to correct it by killing Ace , and orders Kurtz to do so as soon as possible . Meanwhile , Gower is in solitary , but Kurtz is overruled regarding Ace , and she is returned to her regular cell . She is confined there except for mealtimes . At mealtime she meets Wilkins , who is bragging about having backed out in a timely manner ; she is not convinced , and accuses him of betraying her and Gower . Schafer stops the resulting disturbance and returns her to her cell , but Tim is left to the mercies of the angry prisoners . The Doctor is put in the cell beside Gower ; when he learns that Gower ’ s window overlooks the courtyard , he passes a message via Gower to Ace . It contains information that Ace can pass to Kurtz at their next encounter , which exposes Klein as a traitor . Kurtz checks Klein ’ s identity papers , which the Doctor has changed to more obviously expose their forged nature . Kurtz returns them without comment , but the Doctor knows he will verify them later , and act accordingly . Klein now has a deadline , and fears returning without the Doctor , as she took the TARDIS without permission from her superiors , and with the help of her assistant , Schmidt . The Doctor reminds her of the paradox she ’ s creating if she takes the earlier TARDIS , but she dismisses it ; history already records that the Doctor escapes Colditz , only to return to Germany in 1955 , and be subsequently shot and left for dead ; she can use the TARDIS to locate her own version , then return the earlier version to the castle in 1955 , and the paradox will be averted . She takes the Doctor to the command centre , but is intercepted by Kurtz , who tries to arrest her . Meanwhile the Commandant wants to question Ace and Gower , and sends Schafer for them . En route , Ace hears Tim in pain in his cell , and gloats over him , saying he got what he deserved for his betrayal ; this prompts an outburst from Schafer , who is now cold toward Gower . They hear gunshots in the command centre between Klein and Kurtz , and the Doctor intercepts them as he escapes from Klein . He reveals that he has discovered it isn ’ t the TARDIS that changed history , but Ace ’ s CD player , which contains lasers that could be studied by the Reich . This led to early uranium refining , allowing the Reich to win the atomic race . Now they must recover the player before they can leave . Schafer tries to stop them , but gives up when the Doctor reminds him of what he saw inside the TARDIS . They search the command centre and recover the CD player . Ace mentions how lucky they were . If Klein hadn ' t arrived , things would ' ve turned out much worse . The Doctor is not so sure it was mere luck . He found Klein ' s mention of using the TARDIS flight logs odd , considering that the TARDIS doesn ' t have any flight logs . The Doctor theorises that he left Ace ’ s body and the CD player here , when he escaped . After departing in the TARDIS , he likely checked the console and realised his mistake . As he couldn ' t cross back on his own timestream , he had to come up with another way to correct the alteration to history . So , he returned to Germany in 1955 , and allowed them to kill him and capture the TARDIS , but then regenerated into his next incarnation , and became the “ Schmidt ” who would work with Klein , manipulating her into travelling back to 1944 . He would then have set the TARDIS to dematerialise after Klein arrived , preventing her from completing her plans . With the CD player in hand , the Doctor and Ace prepare to leave . She uses her recovered Nitro - 9 to cause a distraction , and head for the TARDIS , but Kurtz is waiting there . He says that Klein escaped in a car , but he knew they would come here . The Doctor assures Kurtz that the TARDIS is safe in the hands of the Allies , but it isn ’ t really Kurtz he ’ s talking to ; it ’ s Schafer , who is listening . Schafer orders Kurtz to stand down , but Kurtz shoots him in the shoulder . Gower takes the opportunity to attack Kurtz , allowing the Doctor and Ace to enter the TARDIS ; Kurtz breaks free and follows , but is caught in the closing inner doors . He shoots the console , which causes the ship to dematerialise , killing him gruesomely . Shaken , Gower promises to testify that Schafer did his duty , should it become necessary . After all , after a fashion , they are both prisoners here . Meanwhile , aboard the TARDIS , Ace is also rattled by her experiences , and by Kurtz ’ s death . While she may not be responsible for that , she has some guilt toward Wilkins , who was beaten . Although the timeline is restored , Klein is still at large , with dangerous knowledge . Ace decides she needs to grow up , and she ’ ll start with her name … Ace is young and childish , but Dorothy McShane will be more mature .