The brand-new Shimmering Sands retirement community is a beachfront paradise—until realtor Jessie Beckton plunges to her death from the penthouse suite she’s selling. When the cops rule out foul play, the Retired Detectives agree to step in. They’re certain Jessie was murdered—but how can they prove it when the apartment was locked from the inside?

As the gang pursue their investigation, a host of potential suspects emerge who all have secrets to hide. But just as they seem to be closing in on a culprit, a shocking second murder sends them back to square one.

Meanwhile, former CSI Lizzie’s marriage to ex-DCI Philip suffers a fateful blow. And their partners in crime-solving, Rick and Moira, find their new romance tested when a mystery woman from Rick’s past appears—with a child in tow.

The team must put aside their differences and join forces with a former adversary if they’re to solve the case. But in a deadly game of cat-and-mouse, can they lure the killer into the open before one of them pays the ultimate price?