In this, his third adventure, Professor Andrew Basnett takes a brief break from his usual stomping grounds in the Little English Village, opting to spend Christmas in a Small Australian City instead. He's visiting Tony, an old colleague with a newish wife, and he's barely had a post-flight snack before he's made aware of a cloud hanging over the marriage. Jan, Tony's bride, is widely believed to have bashed her first husband over the head, and though she was acquitted of the murder, Tony himself is starting to have uncomfortable second thoughts. Things don't get any more comfortable when, at a family dinner, one of the guests is done in, killed with a chunk of the same crystal that put paid to Jan's first husband. And Jan herself? She's disappeared. Only the Professor, it would seem, can banish the clouds of distrust and reveal the truth, clear as crystal.