The Keeper’s Necessary Wife. The Greyhaven Beacon Mysteries, #3

At Greycliff Lighthouse, every light is meant to tell the truth. Government inspector Hector Dunvale arrives on the stormbound northern coast with the power to close Greycliff, dismiss its keeper, and seize the records Elspeth Arden has spent months protecting. An obscure charter offers one narrow defence: the lawful wife of a lighthouse keeper may serve as his recognized assistant. Amos Fenrose offers Elspeth a marriage of convenience.
Their agreement protects her income, property, authority, and freedom to leave. It also carefully avoids stating what either of them wants beyond the law. Elspeth refuses to promise a future she cannot prove. Amos would rather prepare for her departure than risk making desire sound like obligation. Then Dunvale is found dead beneath the lighthouse stairs. The locked tower, a counterfeit key, and Amos's public quarrel with the victim make the newly married keeper an immediate suspect.
Yet the injuries on Dunvale's body suggest he was killed elsewhere and carried into Greycliff through a forgotten service passage. As Elspeth searches corrupted payrolls and Amos examines altered machinery, they uncover a trade in stolen lighthouse prisms. The thieves have hidden their shipments behind the names of dead keepers' wives-and assembled the missing glass into portable beacons capable of luring ships onto the rocks.
With a violent storm approaching and a false light already flashing above Wrecker's Reef, Elspeth and Amos must expose a murderer before another vessel follows the fatal signal. But the investigation is not the only danger to their uncertain marriage. Legal vows have made them husband and wife. Desire has made the agreement impossible to dismiss as mere necessity. Now they must decide whether honesty requires certainty-or whether two guarded people can choose each other without knowing how their story will end.