Titus Alone - Mervyn Peake (Book 3 in The Gormenghast Trilogy)

Titus Groan, now almost twenty, escapes from Castle Gormenghast, flees its oppressive Ritual, and becomes lost in a sandstorm. Helped by the owner of a travelling zoo, Muzzlehatch, and his ex-lover Juno, Titus ends up stranded in a big, bustling city. No one there having heard of Gormenghast, the general consensus is that the boy is deranged, and with no papers, he's soon arrested for vagrancy.

But there are a few people who believe in his story, or at least who are intrigued by it, and they try to help him. And now Titus, the deserter, the traitor, longs for his home, and looks for it all the time to prove, if only to himself, that Gormenghast is truly real.