James and Danielle come across each other at a fancy hotel in France. They spend four days eating and making love. James is a spy but pretends to be a water engineer. He's descended from Thomas More, whom he can quote, in a limited way, during dinner. Danielle is a high-flying, deep-diving oceanographer, who insists there is no such pursuit as "oceanography"  it's merely a congregation of scientists from different disciplines turning their attention to the ocean. After their tryst, she's off on the gay carousel of international research: meaning, loyalty and responsibility seem limited among these blenderised intellectuals and scientists, "industrial collaborators" whom she vaguely distrusts. She is pretty vague about everything.
James goes to Somalia and is taken captive by an al-Qaida cell in Kismayo. The ostensible subject of Submergence is jihad: specifically what Ledgard suggests is an amateurish, misconceived jihad that has ruined the nation and people of Somalia, a place for which he makes a passionate, if strangled, plea. During months of being moved from hiding place to hiding place, James tries to work out the differences and similarities between himself and his captors. The jihadists, mostly illiterate boys, come off badly in the comparison. After all, he's a chap who grew up in a big house in England and has read a lot of books and frequents hotels where he romances female intellectuals. James More starts to sound like James Bond, whereas we'd prefer him to be a man out of Javier Marías's more worldly study of government operatives. For all his western concern and conceits, his book-larnin', James can't really have a debate within himself: he can't imagine anything besides escaping to a bath and a cocktail in a fancy hotel in Kenya.
Ledgard's previous novel, Giraffe, about the awful fate of a herd of giraffes in communist Czechoslovakia, was politically and poetically arresting  razor sharp. He seized on an odd moment in human, animal and environmental history, and told us exactly how and why it was so frightening. He is a clever, insidious writer, who uses his own obsessions in the service of ideas and important questions, such as an eerie description, in Submergence, of al-Qaida fighters bathed in the colours of Walt Disney's Bambi  the only entertainment allowed them other than DVDs of beheadings. Submergence is different, a risky book, with shards of Coetzee, Irwin, Grass, and even Bernard Wolfe  not all of them good. It tries to deal perhaps too globally with belief and hard biological fate.
The hadal zone, the very deepest of marine abysses, is Danielle's speciality. Way down there in the dark where we and capitalism (and Islam, come to that) have yet to penetrate, there's an indestructible ecosystem which will go on no matter what we do upstairs with our missiles and our Monbiots. James clumsily ponders a range of metaphors for the abyss: the soul, without the light of religion (James is a believer); the blackness of anarchy and terrorism; the vacuum which will obtain when we and our ideas have been minced by mini-hagfish under the lip of the continental shelf; and  wait for it  the tripes of a whale that swallowed another notable ancestor that James conveniently had.
When Submergence is not a lecture (do we really have to be reminded who Karen Blixen was, or told the ocean is being fished out?), and when it is not a rolling news soap opera, it is fascinating. But it is not a novel. It shouldn't have been let out of captivity yet. There are too many random arty anecdotes and memories which feel personal to Ledgard, not to the characters we're supposed to care about. Danielle thinks and says so little, in fact, we're startled when confronted quite late in the story with a passage like this: "She had to come up with methods of counting the methanogens, the hyperthermophilic autotrophic iron reducers, and the peculiar states and leagues of archaea and bacteria. She had also tried to identify the boundary which separated the living part from where there was no life and to understand the percolation between existence and nonexistence" Of course we sympathise.
It's a relief to be told that the earth and its "true" riches will never be affected no matter how we botch things up. But Captain Nemo, who strangely gets a kicking here, said a lot of this more elegantly and appealingly in 1870. Meanwhile, we have to live in the part of the world that Danielle doesn't care about, and James cannot get to grips with, and damn it, we're going to die here, without much help from these two.
Todd McEwen's Who Sleeps With Katz is published by Granta.