Roots: Colditz and Latter Days at Colditz (the books by R. P. Reid), the film The Colditz Story (1955), the 1975 BBC/Universal TV series, and the board game by Holdson), The Terminator (a time traveller from the future returns to the past, creating a time loop), Galactica 1980 (scientist from advanced civilisation giving Nazis futuristic technology). Ace mentions the Stone Roses.
Intertextuality: Ace listens to Danny Pain on her walkman, first mentioned in Paul Cornell's New Adventures No Future and Happy Endings.
Goofs: Kurtz is constantly referred to as an officer, yet as a Feldwebel his equivalent rank is sergeant, an NCO, not an officer.
Some lines are obscured by the background effects.
Upon arriving in the courtyard, the Doctor and Ace are shouted at in German. (i.e. this is not translated) [This may be due to the TARDIS having recently hit an anomaly in the vortex and is righting itself. Alternatively, perhaps as 'hande hocht' and 'schnell' would be familiar phrases to Ace from her own popular culture, there was no need to translate them]
There is no logical way German scientists - no matter how clever they thought they were - could possibly use a laser to speed up the development of nuclear technology. Ace's CD walkman is made of 1990s (not to mention broken!) components that would have completely baffled them - how would they even know what it was, let alone get it to work?
Ace explains that the TARDIS had disappeared when the Doctor and Klein went to look for yet, yet can't have known this as she wasn't there, nor was the Doctor able to tell her.
And don't even get us started on the paradoxical fact that Klein's future history of 1965 is 'erased' so therefore the chain of events in 1944 never took place (q.v 'Day of the Daleks', 'Carnival of Monsters', 'Pyramids of Mars', 'The Mutant Phase', 'The Curse of Fenric' - so we're not going to bother mentioning it).
Double Entendres: The Doctor orders himself to be physically examined: 'Put your hand here. Now here... impossible yes - isn't it?'
Dialogue Triumphs: 'I believe I can hear your Golden Age crumbling'
'There's no need to take it out on the cutlery.'
[How do they get messages from solitary confinement to others?] 'My cell looks over the courtyard. I'll shout out to someone.'
Continuity: Klein is from the year 1965 in an alternative time line in which Nazi Germany wins the Second World War thanks to laser technology gleaned from Ace's captured walkman (enabling then to refine uranium and develop nuclear weapons). In that time line, Ace is killed trying to escape Colditz, and the Doctor flees in the TARDIS, returning in 1955 when he is shot by the SS and left for dead, regenerating later - although they are fearful of the machine's technology the Nazi's do not use the TARDIS. In 1965 Klein, with the assistance of another who calls himself 'Schmidt' (presumably an alternative eighth Doctor - see 'Links'), finds the ship's flight logs and programs it to retrace one of its most recent journeys, to 1944 ('Schmidt' meanwhile programs it to dematerialize after she arrives, trapping her there).
The TARDIS hits an anomaly in the vortex (likely Klein's TARDIS traveling back to 1944).
The Doctor is shot in the shoulder but heals overnight, his bullet 'working its way out' of his body.
Ace's rucksack contains a rope ladder and explosives, and her CD-walkman came from Paul Tanner in the 21st Century (see: 'Links'). She determines to be called Dorothy McShane (or simply 'McShane') from this story on.
Links: Silver Nemesis ("I hate Nazis."), The Fearmonger' (Paul Tanner), 'Dragonfire', 'The Curse of Fenric' (Ace's rucksack and rope ladder), 'Storm Warning' (the Doctor's German alias). Klein is reunited with the Doctor in the 'Klein Trilogies' and UNIT: Dominion.
Location: Colditz Castle (Oftlag 4-C), October 1944.
The Bottom Line: As Nazi Germany is a setting that has been well trod before by the series in other media (notably the New Adventures Timewyrm: Exodus and Just War), 'Colditz', it could be argued, starts off on its back foot. The addition of an intriguing time paradox the rest of the story somehow isn't as engaging as it would like to be - perhaps we need to know more about Klein or her world? Even the Doctor and Ace... sorry, Dorothy - fail to treat the prison and its staff that seriously.
ACE IN TIME
There are three Aces, or perhaps it is more correct to say that there are three Dorothy McShanes. The earliest audio placement of Ace falls within the 'lost' Ace, Seventh Doctor and Raine season, and generally follows the character of Ace established by the TV series. The TV series' characters Big Finish feature of course have, in some other media, already been reinterpreted by non-audio or TV adventures; Ace shucked off her teenage self post-TV series to mature and harden through Virgin's New Adventures line. It is this version of Ace, broadly speaking, which develops with the Doctor and Bernice Summerfield in the three audio stories featuring this TARDIS crew, plus the Companion Chronicle The Prisoner's Dilemma (which also suggests that Ace travelled some time apart from the Doctor and Bernice and later returned to their company). A version of Ace with battle experience and some knowledge of futuristic technology also informs Enemy of the Daleks, and for many listeners it appears that in order to accommodate such dramatic changes in Ace's character, her time with the Doctor and Hex must therefore fall after her time with the Doctor and Bernice. This also suits the Bernice stories, too, as Love and War (being an adaptation of an early New Adventure itself) concerns an emotional arc for Ace that brings to an end her teenage outlook and introduces her aforementioned 'hard' adult identity. Finally, it is this version of Ace, or perhaps an interpretation of it, that best describes the Ace who for a time renames herself 'McShane' in Colditz and comes to meet Hex and travel with him and the Doctor shortly afterwards.