Mortal Leap is not exactly a thriller, not exactly a philosophical inquiry, not exactly a character study ... but in some ways all these things. The protagonist tells the story in the first person and appears to be a "reliable narrator", but there is a lot he doesn't know or understand. He's always trying, though. He philosophizes frequently about life, what the universe expects from us, what we owe to our fellow humans. For him, the answer to that last question is -- nothing. We don't owe anyone anything; we live for ourselves. Our narrator is a misfit, not a psychopath or a criminal, but a taciturn, apathetic loner. As you might expect, he will have a character arc.
The basic story: The narrator runs away from a strict Mormon household at age 17, during the Great Depression. Soon he is a merchant seaman on the Pacific. Aloof, indifferent, and uncommitted, he has a hard-scrabble existence: the only women in his life are prostitutes; his only "friend" is Victor, an embittered older seaman who betrays the narrator more than once. It seems that Victor is what the narrator is fated to become, 30 or 40 years down the road.
The story advances to World War II. The narrator is now the engineer on a fourth-rate cargo steamer, crewed by criminals, losers, and misfits -- and Victor, who got him the berth. After a series of adventures, the rust-bucket ship, carrying munitions for the war effort, blows up in the Solomon Islands. Our narrator is cast away, and gets caught up in the periphery of the battle of Guadalcanal, raging nearby. He tries to make it to a damaged American destroyer. It sinks as he reaches it. Burned, exhausted, he almost dies in the water ... but awakens to find himself in a US Navy hospital.
The navy mistakenly believes he is one of their own, assuming he was on the sunken destroyer, but they can't figure out exactly who he is. His hands and face are burned, and he presents medically with amnesia -- he is essentially unidentifiable. An intelligence officer and a navy psychiatrist ply him for weeks, trying to ferret out his supposedly lost memory, or at least raise him out of his profound apathy. They fail, and his case appears hopeless ... then a mysterious dark-haired woman, apparently wealthy, comes into his hospital room and identifies him as her missing husband.
The woman's enigmatic impulse to falsely claim him (this is the mortal leap of the title, or one of them), is the crux and turning point of the story. From here, the narrative follows them and their strange but somehow tender game of a relationship, while probing the complexity of human motive, and the nature of personal identity.
Harris is an adept writer: the characters are interesting, the physically adventurous parts are involving, and the psychological/philosophical adventure even more so. The narrative is never slowed down by the philosopy. This is ultimately a very satisfying novel. It offers both entertainment and substance.