Police chief inspector Bamford Alan Markby and his friend Meredith Mitchell, at a prestigious flower show in Chelsea, run into Meredith’s school friend Rachel—who turns out to be Alan’s ex-wife as well. Rachel’s new husband, Alex, suggests celebrating the meeting with champagne, but he gets pricked by a thorn from some plant, feels unwell, and dies a few minutes later in his luxurious car. The forensic examination establishes that the thorn was poisoned—which means that Inspector Markby and Meredith are at least the key witnesses to the murder…