Siobhán is a brilliant young marine biology student, more at home amidst laboratory equipment than people. As a component of her studies, she boards a trawler overseen by a couple whose amiable demeanour shields both financial worries and profound grief. Siobhán is not exactly welcomed aboard: her cool, scientific perspective is at odds with that of the salty, superstitious crew of ‘fishmen’, and her red hair is considered bad luck. Not long after setting sail, the old ship’s hull is glommed onto by a bizarre, bioluminescent creature of unknown genus.