Roots: Fatherland. The Doctor wilfully misquotes a Monty Python sketch. There are extracts from Karl Muller's Ballots, Blood and Bullets - Political Chaos in Post-War Germany and General H. Popplewell's Reminiscences of World War II. There are references to Dixon of Dock Green, Sherlock Holmes, Fiats, Quasimodo, and Laurel and Hardy. The Aliens were first referred to as the War Lords in Malcolm Hulke's novelisation of The War Games.
Goofs: The prologue is dated 25,000 BC - referring to Timewyrm: Genesys. However, that book was set circa 2,500 BC.
I wouldn't normally be too bothered by differing spellings of names, but Sidney/Sydney Harris has his name spelt two different ways on consecutive pages (12 and 13).
The 1927 textbook quoted on pages 97-98 talks about the Nazis being banned and having killed all hope of lasting political success following the Munich Putsch. However, by 1927 the Nazis were very active, and gaining support in rural areas thanks to an agricultural depression. It also wrongly claims that the words "National Socialist" were part of the party's name when it was founded. It also puts the Putsch in September rather than on the historical date of the 9th of November.
Ace notes that she doesn't speak German, but the Doctor doesn't automatically assume that she's under the control of a malevolent alien entity [more of a Goof of The Masque of Mandragora, but worth mentioning].
Goering's assessment of his rivals on page 114 misses out Rudolf Hess - head of the Nazi party and with the title Deputy to the Fuhrer in 1939 (when this chapter is set). In fact, Hess isn't mentioned at all in the book, despite being one of the most important men in the Nazi hierarchy up until 1941.
The timescale for the conquest of Poland is far too short. Hitler claims that the conquest was practically over within the first two days when Poland actually held out for the best part of a month. Mind you, this doesn't directly contradict the historical timeline. Also, the British ultimatum is referred to as the English ultimatum. Does that mean that Scotland, Wales, and Northern Ireland were never part of the war?
It is implied that The War Games marked the first meeting between the Doctor and the War Chief, which is consistent with the hints in that story, but is contradicted by the subsequently published Divided Loyalties. Also, there are a number of inconsistencies between this story and The War Games, as noted by Adrian Petford in the comments.
Technobabble: Temporal refraction could cause a freak foreshadowing of a TARDIS's departure. Cyclic-recurrent phase system. Highly complex psycho-kinetic-spatio-temporal phenomenon.
Dialogue Disasters: "Spoiling your father's evil schemes was a pleasure."
The Doctor: "How can you think of food with a major temporal crisis on our hands?"
The Doctor: "We come in all sorts, just like liquorice."
Dialogue Triumphs: The Doctor: "Remember you're British, Ace. You're supposed to like taking your pleasures sadly."
Ace: "It's a free country, isn't it?"
Lieutenant Hemmings: "No, I'm afraid it isn't."
The Doctor explains to Ace why she can't blow Hitler up in 1923: "In history, the real history, Hitler's Thousand Year Reich lasted from 1933 to 1945. Twelve years and that was it. Finished. The main reason was that Hitler was an incompetent madman. You blow him to bits and maybe a competent madman takes charge. Someone who really can make the Reich last for a thousand years."
The Doctor: "Changing history is a delicate operation - like brain surgery. You don't start by sawing the patient's head off."
The Doctor: "I'm a wandering scientist and scholar and you're my niece. Be as enigmatic as possible and give the impression that I'm a strange and mysterious character with a number of mystic powers."
Ace: "Just stick to the truth, you mean?"
The Doctor: "Who do we know who's raving mad, racketing through time and space, and obsessed with causing trouble?"
Ace: "Apart from you, you mean?"
Ace: "We're being chased to the top of a tower by a gang of zombies - and your solution is to blow the tower up with an atomic bomb?"
Continuity: Following the events of Timewyrm: Genesys, the Timewyrm decides to seek revenge against the Doctor by tampering with Earth's history so as to destroy humanity. She chooses World War Two as her starting point, but becomes trapped in Adolf Hitler's paranoid mind prior to the Nazi party rising to power in Germany. The Timewyrm takes Lieutenant Anthony Hemmings from the alternate timeline in a replica of the Doctor's TARDIS [or possibly in the Doctor's actual TARDIS whilst possessing the Doctor's mind] (see Timewyrm: Revelation).
The War Chief originally fled Gallifrey because he rose so rapidly in the Time Lord hierarchy that Borusa saw him as a threat and persuaded the CIA to manufacture evidence of treason against him. Following the events of the War Games, the seriously wounded, but not actually dead, War Chief was taken back to the Aliens' home planet as a scientific curiosity. He was thrown into a ship's hold and started to regenerate, but because of his massive injuries, extensive tissue damage, and lack of medical care, the regeneration aborted, leaving him a white haired, white bearded old man with vestigial extra limbs and a distended skull. He survived on the planet of the Aliens and convinced the son of the War Lord, a virtual double of his late father, that he wasn't, and never had been, a traitor and that his treachery had all been a misunderstanding. Seeking revenge against the Doctor, he helped the Aliens to find a way to penetrate the force barrier that the Time Lords had placed around their home planet, and convinced them to launch another plan to conquer the galaxy using humans, this time from Earth. Using time-scanning equipment provided by the War Chief, they found the Third Reich and decided to make use it, helping Hitler to win the war and establish an empire for them [it is implied that they also have time travel, probably, like the SIDRATs, based on the War Chief's TARDIS]. They intend to provoke war between Russia and America to remove them from the picture. They also intend to give the Reich nuclear power to destroy its opponents. The War Chief also knew that the Doctor would notice any alteration in the history of Earth, thus prompting him to investigate.
The War Chief hides his deformities under a black cloak and carries a silver-headed cane containing a concealed laser weapon. He intends to transplant his brain into the Doctor's undamaged body. The War Chief adopts the alias Doctor Felix Kreigsleiter, der Kreigsleiter being German for "the War Chief". Kreigsleiter becomes head of the Aryan Research Bureau, a cover for the War Lords' project. The Aliens from The War Games refer to themselves as the War Lords. They use psychic amplification to improve Hitler's oratory at the Nuremberg rallies, implying that they contributed to his rise to power (the Doctor notes however that the presence of the Timewyrm in Hitler's mind made their task easier). They use transmat booths and have the technology to precondition SS troops to serve them. The War Chief extends this technique over some of the troops to allow him to reanimate their corpses using his own will power. The War Chief is killed when the Doctor overloads his nuclear reactor, causing a nuclear explosion that destroys Drachensberg Castle.
The Doctor has a variety of coins and a pencil-sized torch in his pocket. He knows a Venusian nerve pinch that renders someone unconscious with short-term amnesia. He speaks "fluent everything" - including German. He has a gadget [Stattenheim Remote Control] which can park the TARDIS in the space-time continuum. He also has a device emitting a high frequency sonic pulse, making him unbuggable and a Gallifreyan Army Knife marked as property of Castellan Spandrell (from The Deadly Assassin). He admits that he loves Ace [though what this means for a Time Lord is anyone's guess - see Human Nature (book)]. Whilst in the alternate timeline, the Doctor uses a "standard Gestapo technique" to frighten off two BFK members by convincing them that he is a Gestapo officer. He later poses as Reichsinspektor-General Herr Doktor Johann Schmidt and uses the same alias when he becomes one of Hitler's advisers in Nuremberg in 1939. He carries a handful of assorted change in his pocket, as well as a monocle on a black ribbon. He and Ace share an elaborate cold collation with champagne whilst posing as high-ranking Nazi officers. He dons a long black leather overcoat and a black soft hat. Kreigsleiter later forces him into a hooded black robe. He has a pot of ointment in the TARDIS containing Elixir of Life (The Brain of Morbius); the label reads, in Old High Gallifreyan, "Dr Solon's Special Morbius Lotion. Guaranteed to Contain Genuine Elixir of Life. Manufactured Under License by the Sisterhood of Karn."
The TARDIS is resistant to being painted. The paint just falls off. [The Doctor presumably turned this feature on after The Happiness Patrol, when the paint stayed on.] The Doctor is able to summon the TARDIS via a thought impulse to the telepathic circuits (he adds a whistle as a flourish), although erratically it materializes three feet above the ground and floats there. The Doctor has a copy of The Day by Day Almanac of World War Two in the TARDIS. He converts an old lantern into a telepathic relay, boosting the power of the TARDIS force field to free the Timewyrm from Hitler's mind and temporarily dissipate her.
Ace has found the time to make up a new explosive called nitro-nine-a - twice the whammey of normal nitro-nine at half the weight (i.e. four times as concentrated). It is made in the form of glass-like marble-sized spheres and detonates when it receives a severe impact and it needs to be thrown rather than dropped in order to explode. She skived off most of her German lessons and never took the exam. She is not a virgin. Whilst in the alternate timeline, Ace poses as Dorothy Schmidt, the Doctor's niece. She eats a full English breakfast, plus toast and kedgeree. Hemmings backhands her a cross the face, bloodying her nose and upper lip. She is able to resist the hypnotic spectacles of the Aliens. To her disgust, she faints with relief when the Doctor arrives at Drachensberg Castle. She later brandishes a machine gun, spraying bullets at Kreigsleiter's conditioned SS troops, and later uses grenades to dispatch the reanimated corpses.
The Sisterhood of Karn only make one pot of sisterhood salve once every hundred years. A little dab is all you need to heal an injury. The Doctor has the dregs of a jar left.
The alternate timeline split off at the battle of Dunkirk, with the Nazis capturing the port and the remains of the British Army. Goering's Luftwaffe won the Battle of Britain, and Operation Sealion succeeded in capturing Britain when a freak storm sunk most of the British Navy. As a result, the Nazis won the Second World War. The British Government went into exile in Canada. Joseph Goebbels' The Thousand Year Reich - The Glorious Beginning is published in 1947 in this timeline in which . Churchill was executed as a war criminal. Edward VIII is allowed to marry Wallis, and signs a Treaty of Accord, establishing Great Britain as a protectorate of the German Empire. Sir Oswald Mosley becomes Prime Minister. The Britischer Frei Korps, or BFK, whose authority stems directly from the Third Reich, polices Britain.
Links: Timewyrm: Genesys. There are several mentions of The War Games. Ace mentions Commander Milligan's base from The Curse of Fenric. She also has a dream featuring a Dalek (Remembrance of the Daleks. The Doctor mentions the Meddling Monk (The Time Meddler, The Daleks' Master Plan) and the Gallifreyan Hermit (Planet of the Spiders). He has some Sisterhood Salve (The Brain of Morbius) in the TARDIS. He says that he was once in danger of being washed down a plughole (Planet of Giants). He mentions his time at UNIT and the low cunning and high treason amongst the Time Lords.
The Doctor also mentions Flavia (The Five Doctors) and Borusa (The Deadly Assassin, The Invasion of Time, Arc of Infinity, and The Five Doctors), as well as having a Gallifreyan Army Knife belonging to Spandrell (The Deadly Assassin). The Doctor again claims, "Sleep is for tortoises" (The Talons of Weng-Chiang).
Location: London, England, and New Berlin, Germany, 1951, in an alternate timeline; Munich, Germany, 1923; Nuremberg, the Berlin headquarters of the Gestapo, and Drachensberg Castle, Germany, 1939; Felsennest, Germany, 1940; and London, England, 1951.
Future History: Humans will learn the psycho-dynamics of crowds at some point after the twentieth century.
Unrecorded Adventures: The Doctor claims that this is the first time he has met Hitler. [This will turn out to contradict the sixth Doctor novel The Shadow in the Glass
The Bottom Line (prosecution): 'If Hitler had won.' Timewyrm: Exodus is a good exploration of the theme of Nazis winning World War 2, and someone trying to put history back on track. It has a strong plot and good characterisation of the Doctor and Ace, the Nazi hierarchy, and the characters invented for the book. Its weakest point is its style, which is best described as competent and, for me at least, has the effect of obscuring all the positive aspects of the story. It has a very good reputation amongst fans, but in my opinion is usually overrated.
The Bottom Line (Defence): 'Who do we know who's raving mad, racketing through space and time, and obsessed with causing trouble?' 'Apart from you, you mean?' Terrance Dicks' first original Doctor Who novel is also his best, an engaging story that manages to ally the Doctor with Hitler without becoming tasteless. Much like Timewyrm: Genesys, it isn't really too broad or too deep for the small screen, but it is thoroughly entertaining and has aged better than Dicks' subsequent novels.