"Tomcat" is, although narrated by a Vietnam war vet, definitely more lighthearted than I assume O'Brien's other books to be. Although injected with humor and wordplay in varying shades between the subtle and the ridiculous, it is still somewhat horrifying in its own tongue-in-cheek way. The reader is treated to a fascinating, front-row view of the main character's descent into near madness.
Thomas H. Chippering, the "Tomcat" of the title, slowly twists his life into a chaotic shambles because of his unrelenting obsession with his ex-wife, coupled with his opinion of himself as a handsome and attractive ladies' man (an opinion which, unbeknownst to him, is not shared by women in general). Chippering's life has been a series of betrayals, each of which he sees as a personal affront and each of which he feels more keenly than the one before. It is not until he hits rock bottom that he takes the time to look around and see that he is not alone. He is lucky enough to have the opportunity to rebuild his life--perhaps not into the life he thought he wanted, but into something that probably suits him better, anyway.
The book had a promising beginning (with the ridiculous, in 1952, when young Tommy's dad brought home a turtle named Toby rather than the airplane engine Tommy had been hoping for) but the rest of the story didn't turn out to be what I expected based on that first chapter. Nor were any of the characters especially likeable, but this turned out to be acceptable, because somehow the reader is not expected or required to like the characters.