Relentless

exhaustion, Penny took a nap. Because she did not want to be in a bedroom, apart from us, she curled in the fetal position on a family-room sofa, facing the harbor, hoping the movement of the water and the gliding boats would lull her to sleep.
    Milo returned to his computer and other gear on the coffee table. He sat with his back to the harbor.
    By his side again, Lassie lay on her belly but with her head lifted, ears pricked, facing the windows. Perhaps the kiting seagulls and the occasional formations of brown pelicans intrigued her.
    At the kitchen secretary, I used Penny’s laptop to go online. I needed to learn more about how John Clitherow’s family had died.
    I dreaded discovering another multiple murder with details to freeze the marrow. What my search string led me to instead was a story without blood but no less disturbing.
    According to press reports, Tony and Cora Clitherow, John’s parents, had lived lakeside in Michigan. They rented a slip at a nearby marina, where they kept the
Time Out
, a Bluewater 563.
    Exploring the company’s website, I found photos of a craft like theirs. The low-profile, double-deck cruiser featured an upper helm station enclosed by a hard top and canvas walls. This sleek, handsome boat included a main cabin with galley and two staterooms with baths.
    On that Thursday in late June, three summers previous, Tony and Cora had taken the
Time Out
for a day trip. With its amenities and range, the boat could overnight on water. But they had told the owner of the marina, Michael Hanrahan, they intended to return before dusk.
    When they didn’t dock by nightfall, Hanrahan was not concerned enough to report them missing. On a couple of prior occasions, they had made impromptu changes to their trip plans.
    The next day, when the Coast Guard could not raise the
Time Out
by radio, a search was launched. At 4:10 in the afternoon, by its transponder signal, they found the boat adrift, five miles offshore.
    Tony Clitherow sat belted in the chair at the upper helm station, naked and dead. The cause of death was not apparent.
    A search of the vessel did not turn up Cora.
    At the stern of the boat, a taut cable stretched from the gin pole into the water. With the windlass, they reeled in the line.
    They pulled Cora from the lake as if she were a fish. She wore nothing but handcuffs. The windlass line entwined the chain between the cuffs and encircled her waist, secured to itself with carabiners.
    She had been dragged through the water for many miles, no doubt at night when people aboard passing vessels would not see her.
    Cora’s challenge had been to avoid drowning as she cleaved facedown through the Bluewater’s wake. Secured in such a way that she was unable to turn onto her back, she would have been repeatedly pulled under by turbulence, would have repeatedly broken the surface, striving always to keep her head up, gasping for breath.
    Exhaustion defeated her. Although not a speedboat, the
Time Out
was capable of enough knots to make being towed through choppy water a punishing experience. Feathery bruises covered her body.
    The continuous impact of the water or abrasive debris in it wore away her left eyelid. Both eyes were as frosted as etched glass.
    An assessment of Tony’s guilt would ordinarily depend on the coroner’s report. But the autopsy proved inconclusive.
    The quantity of alcohol in Tony’s stomach and the percentage in his blood suggested that he could have died from alcohol poisoning. If he had been that drunk, however, he surely would have at some point vomited on the deck or on himself, which he had not done.
    The homicide detective on the case, Warren Knowles, had resisted a determination that Clitherow killed his wife. Knowles argued that a tear at the corner of Tony’s right nostril and a facial bruise raised the possibility he’d been restrained while a tube was fed through his nose and into his throat for the administration of alcohol by force.
    In the opinion of the medical examiner, those injuries had more likely been sustained in a drunken fall or when Cora tried to fend off her husband as he sought to handcuff her.
    Knowles also raised the possibility that the alcohol had been administered to cloak the true cause of death and that Tony might have been killed by an air embolism, a bubble that, injected into his bloodstream, traveled eventually to his brain. At a hearing, the detective spoke of a suspected needle puncture.
    The medical examiner felt that