IMAGINE YOU ARE a celebrity harboring a secret that could make you a national pariah overnight. One day the phone rings, and a young woman representing a mysterious online publication called the Moral Foundation informs you that her organization has learned of unseemly behavior committed by you or someone close to you. No details, no chance to review the evidence, just a date on which the website plans to post what it knows. The only way to stave off public ruin is to provide credible evidence of wrongdoing by someone else you know. The caller gives you a phone number and a private account number, and hangs up.

What do you do?

If you are Ritchie Shepherd, the central figure in James Meek’s novel The Heart Broke In, you stew and stew. A washed-up British rock star enjoying a second career as producer of a reality TV show called Teen Makeover, Ritchie guards an incendiary secret: he carried on a months-long affair with an underage contestant on his show. If word gets out, Ritchie stands to lose his career and his marriage, and could face charges of statutory rape. But he’s keenly aware that, if he can bring himself to betray a family member, the Moral Foundation might be interested to learn how his sister Bec, famous for discovering a possible cure for malaria, became pregnant — despite the fact that her live-in boyfriend Alex is infertile.

Ritchie’s clash with the Moral Foundation is only one of many threads that wind through this sprawling social novel, but it is the one that best dramatizes the issue at the heart of the book: how modern societies regulate sexual morality when scientific progress in the realm of human reproduction has created a culture of promiscuity without consequence. Meek, a former foreign correspondent for Britain’s Guardian newspaper and author of three previous novels, skillfully interweaves Ritchie’s celebrity milieu with the world of cutting-edge science occupied by his sister Bec and Alex, a fellow researcher who may have stumbled upon the scientific answer to the Fountain of Youth. Also in the mix are Alex’s brother, Dougie, a ne’er-do-well Scottish postman; Bec’s spurned fiancé, Val Oatman, a former newspaper editor turned online moral scold; and Gregory Shepherd, Ritchie and Bec’s father, a British soldier made famous during the Irish Troubles, when he was executed for refusing to give up the name of an IRA informant.

Meek eventually ties together these disparate strands, but it takes him a good long time to get there, and some readers may give up on the novel before he does. This would be a shame. The Heart Broke In may be a “loose baggy monster” in the Jamesian sense of a novel that takes on more than its dramatic structure can carry, but along the way Meek offers keen insights into the shifting mores of a society in which so many of the limitations on longevity and fertility have been eradicated by scientific discovery.

The Heart Broke In is a novel about sex — not so much the act itself, but its significance in a world where its original purpose, the propagation of the species, is being rendered obsolete by science. At one end of this exploration is Alex, whose cancer research has uncovered a mechanism within human cells that he calls “the chronase complex,” which spots signs of premature aging in other cells. This has obvious implications for research into cancers whose cells grow at different rates from normal cells, ...