There is a restaurant in Manhattan's Upper East Side where a staff of 37 identical twins serve up twin burgers, two-for-one drinks and complete each other's sentences. The doors have double doorknobs, the bar stools are joined at the base and the menu offers twin quarter-pound lobsters on "Twosdays".

Reading Richard Kearney's second novel is a little like entering such a demented theme park. Everything is doubled up.

Walking at Sea Level is a sequel to Kearney's debut novel, Sam's Fall. The eponymous Sam is Sam Toland, a monk, who is drowned and whose twin, Jack, is maimed in an accident at the hands of the twins' mentor, Abbot Anselm.

Time has moved on. At the start of this novel, Jack Toland is struggling with his doctoral research at a university in Montreal, he is separated from his wife, Raphaelle, and daughter, Emilie, and he is drinking heavily and smoking too much dope.

The subject of his research is an obscure 18th-century Irish scientist, and Jack's namesake, J.J. Toland, whom Jack believes belongs with the best of the celebrated rationalists - Descartes, Spinoza, Leibniz and Locke. But his main obsession is not his research. No, Jack is still haunted by the suspicion that his twin brother slept with his wife before his death.

He is called forth from his snowy isolation by a letter from Raphaelle in which she says she is going away for a while and pleads with him to come to Geneva where she is living with Emilie to look after the child he has not seen for five years.

Answering the call, Toland travels to Switzerland and takes over the care of his truculent 10-yearold daughter, and the two of them set out to find Raphaelle, who has disappeared.

In the course of his search, Jack discovers that his estranged wife is writing a book about twins, thus fuelling his narcissistic speculation that she was, in fact, in love with his dead brother, Sam.

The reader, therefore, is not only treated to wads of Jack's doctoral thesis but also has to wade through Raphaelle's unfinished manuscript as well. All very post-modern.

At one level this is an old-fashioned quest, a detective story where the clues are in research papers and libraries rather than in smoky bars and back-alleys. And at that level Walking at Sea Level works. Kearney has a nice, pacy style and the narrative moves briskly along in between the instructional extracts from the protagonists' scribblings.

There is a tendency to melodrama, though. Jack, being Jack, suspects that Raphaelle has run off with a man. The truth is much more outlandish, a kind of Fifties re-run of Sophie's Choice and some more unlikely twinning, I'm afraid.

Another sub-plot involves an extraordinarily cavalier treatment of child pornography which is pulled out of the hat towards the end of the novel and dropped as quickly in favour of Jack's persistent obsession with his wife's infidelity. Kearney's is not an Irish novel in its theme or its concerns. Set in Montreal, Paris and Geneva, it is a book that struggles with large ideas - the notion of God as a dual entity, the human impulses of good and evil, the Gnostic theory that the only way to reach God is to embrace the worst excesses of degradation.

But all of its obvious erudition weighs the novel down. The novel form needs characters as well as ideas - characters to whom, at the very least, the author is committed. The child abuse strand of the novel, for example, centres around Toland's daughter's friend, Margarita, but she is such a slight, one-dimensional creation, and is abandoned so summarily, that she remains transparently a plot device in the form of a handy baby-sitting service while Jack is out on his white charger.

Kearney's intellectual concerns and the knotty, maze-like plotting of the novel owe much to Umberto Eco, but while Walking at Sea Level is clever and competent and learned, it is ultimately without much passion.

Mary Morrissy is a novelist, and an Irish Times staff journalist