Identical twin sisters Alex and Hannah are the owners of Murder and Mayhem, a mystery bookshop that sells their famous poison-themed Killer Chocolates. But now, there's a real killer in their midst. Shortly before Christmas, their septuagenarian neighbor, Jane, confides to Alex that a murderer from a true-crime show has taken up residence in the village. Unfortunately, she's also shared her suspicions with town gossip Netta. The next morning, Alex shows up at Jane's house to watch the show, but instead discovers Jane's body, with a box of Killer Chocolates nearby.

The sheriff quickly zeroes in on two suspects: Alex, a beneficiary in Jane's will, and Zack, a handyman who was seen leaving the crime scene. But Alex maintains her innocence and sets out to draft a list of other potential suspects--townsfolk who'd recently been seen arguing with Jane.

When Alex gets hold of Jane's journal, she begins to understand the truth. But a bearer of ill tidings is arriving early this year--and Alex just might not make it to Christmas.