THE INVISIBLE CODE

Two cases, from different but equally unexpected quarters, emerge for the staff of London’s Peculiar Crimes Unit.

Beloved of fans but reviled by the Home Office, the PCU is being systematically starved for cases by Oskar Kasavian, the security supervisor hoping to diminish its capacity to bring scandal on her majesty’s government. So naturally, Arthur Bryant, the irascible polymath who’s one of the team’s senior members, goes out hunting for cases on his own. He’s fascinated by the death of Amy O’Connor, a part-time bar manager who was found in St. Bride’s Church after suffering a fatal heart attack with no apparent cause. This is the sort of thing we should be investigating, he tells his more sedate counterpart John May. Before they can establish their authority to intervene in a case that’s officially none of their business, another mystery arrives courtesy of none other than Oskar Kasavian, whose much younger Albanian wife, Sabira, is convinced she’s being hounded by evil spirits. Promised the moon (honors and titles, long-range security, freedom from ritual attempts to shut them down or zero out their budget) if they can figure out what’s tormenting Sabira, the PCU team sets to work. But Sabira’s behavior becomes increasingly erratic—she keeps insulting the well-bred wives of her husband’s Home Office colleagues in distressingly public settings—till she finally turns up dead in Sir John Soanes’ House, the legendary London museum, beneath one of the paintings in William Hogarth’s series The Rake’s Progress without a mark on her to indicate how she died. What can her death possibly have to do with Amy O’Connor’s?

Mr. Bryant and a covey of diverse experts expatiate informatively on witchcraft, code-breaking and national defense. But there’s less warmth or humor or real mystery than in The Memory of Blood (2012) and other recent PCU outings.