This books leaves you dazed and amused. That doesn't say it's a good book. In fact, it isn't. It's a fake throughout. It just leaves you as dazed as you would be if you discovered a good friend has been telling you lies all along, and as amused as one feels after having been played a practical joke.
The books' content is a (good, clever, superb, funny, whatever) assemblage of stereotypes and cliches found in (homoerotic) childhood novels (e.g. Gide's Counterfeiters, Julien Green's L'autre Sommeil, Cocteau's Enfants terribles - Fry further "credits" JD Salinger's Catcher in the Rye and Harper Lee's To Kill a Mockingbird). There is no single original ('true') feeling or insight expressed in the book itself - whenever it goes emotional, works of literature are quoted. The author does 'outside' what his fictional character Adrian does inside: cheat and copy, and by reading the appraisals here and on the cover, just as him it seems he's getting away with it.
Now the author tells you on the first page that no word of the following is true. So he has his own 'Liar's Paradox' here, forcing even critics that recognize the book a deceit to admit that it contains some truth. In fact, the book hardly disguises it's a joke, with its absurd spy story frame. My guess is that the author, in the beginning, set himself a spy story outline (with T-shirts and jackets as protagonists), and devoted himself to filling these blanks by characters developed from the sheer impossible other end of a pseudo-autobiographical homoerotic childhood and campus novel. The lingering suspicion that the whole book is an intentional fraud or joke (just look at the dedication line) became conviction when getting to the German conversations in the last slippery slope of events (liars letting liars tell the truth in order to support a lie). The German used here by the philological genius Trefusis quite surprisingly contains wrong grammar and wrong choice of words. That's unlikely accidental. I mean, if one does a debut novel and includes foreign languages, it seems one would turn to some native speaker for possible corrections - that is unless one does in fact want it only to convince the quick reader. Under a scrutinizing eye the book is as 'original' as is the hero Adrian's mock-Dickens "Peter Flowerbuck".
Since it is so obvious the author tries to be discovered the same kind of fraud his hero is, one wonders whether the (then truly 'autobiographical') book hasn't some morals after all. With all the displayed wit, humour, mastery of language, the author seems to say: "See, I could have sold you some enjoyable read without you even knowing everything is second hand - the other bestselling authors do it all the time. I just tell you." That's a liar's morals. The title seems apropriate then (maybe it's even meant to read as part of the author's name, as in "Stephen Fry the Liar"), and since not only this idea is original but also its execution superb, I suppose the book has a well deserved place in literature's monstrosities cabinet.