Paperback: Mrs P's Journey by Sarah Hartley

Phyllis Pearsall is an imaginative choice for a biography. Not only did she research and publish the A-Z of London, walking every one of the capital's 23,000 streets in 1935; she was also blessed (or cursed) with a remarkable family. Her father was a con man and cartographer from Hungary, her mother an unpredictable Irish artist and adventurer who slipped into madness. Hartley has assiduously researched Pearsall's remarkable story. Disappointingly, she has chosen to embroider it with a host of imagined dialogue and conjectural detail.

One of the conversations that Pearsall might have heard during her time in Paris, where she was a friend of Nabokov, is characterised as: "Existentialism. Man and God. Man without God. Art and God. Good God." This conjecture contrives to be both trite and inaccurate, since it refers to café philosophising in the Twenties, a good 20 years before existentialism became the intellectual vogue in Paris.

Pearsall's astonishing feat of mapping is wrapped up in two chapters totalling 20 pages, plus an imaginary monologue. The mysterious metropolitan maze that she tackled, so vast and unknowable, is only briefly mentioned. Possibly, Hartley adopted a novelistic approach to bulk out her raw material or to grab a large readership. Either way, it seems bizarrely at odds with Pearsall's devotion to hard facts and hard pavements that resulted in the creation of the single most important reference work on modern London.

THE AUTHOR is a surgeon and forensic expert who previously alleged, fairly persuasively, that the "Hess" who died in Spandau was a doppelganger. Here, Thomas suggests that the suicide of Himmler in 1945 was equally fishy, but his evidence is much more flimsy, amounting to little more than disappearing duelling scars and dubious dental records. He gives a chilling portrait of the desiccated bureaucrat and his plans for a Fourth Reich outside Germany, but admits that "his true fate will never be known." Thomas points to Kim Philby's belief that Himmler did not die, but the king of double agents is scarcely an infallible source.