Caroline Pargeter, the grand-daughter of the famous botanist Edwin Pargeter, is selling her house and has asked Rosemary and Laura to tidy up the garden. When a mysterious Southern American man is found dead in the Pargeter's back garden, it looks as if there is more to Edwin's seed collection than meets the eye. Rosemary involves her colleague at the Royal Horticultural Society at Kew Gardens to help identify the mysterious seeds before they fall into the wrong hands.