Meet the Blanchard twins: Rose is practical, sharp, and protective. Specialty: manta rays. Finn is too sweet and kind for his own good. Specialty: sharks. They work together on research - but can their scientific minds solve a murder? The cruise ship Dauphin promises luxury suites, a champagne brunch on the Arctic ice - and scientific experts studying the animals of the far north. Rose Blanchard will pilot the ship's spherical submersible, Mouette, while her brother Finn films his beloved Greenland sharks. But when they resurface from a deep-sea expedition, they find one of their colleagues dead - murdered on the ice with a harpoon that should never have been on board. The Blanchards' submarine trip rules them out as suspects, and soon they are asked to turn their scientific minds to investigate the crime. No-one liked the murder victim - but did anyone have a motive strong enough for murder?