When wine critic Ambrose Hauser invites Liz Bartholomew to a prestigious tasting event, she is thrilled. Joined by her locksmith husband, Cy, she spends the event's first day sipping and grading wine. That evening, the Bartholomews join the critics on a boat excursion and a twilight swim.

Ten people descend into Lake Monona. When it's time to return to the boat, one swimmer, a wine critic named Carpenter Dalbesio, is missing. The next morning, divers find the woman at the bottom of the lake, her throat cut.

There are no witnesses, and few clues. The police can't even identify a suspect with a persuasive motive for wanting the woman dead.

As the tasting continues, the critics worry about their safety, and Cy and Liz grapple with the woman's death. The Bartholomews become convinced that there is a secret which explains how and why Carpenter Dalbesio was murdered.

Can Cy and Liz unearth the secret and find the killer?