Helter-Skelter — Patricia Moyes

Cat looked forward to a great vacation sailing with her friends Tim and Dick. But her carefree plans ran aground when the trio spotted a mysterious red-haired object in the water. Cat thought it was a body.

But the police were not convinced, so Cat started off on some private sleuthing of her own. She learned that there had been a leakage of secret information at her uncle's naval research station, and she uncovered a baffling mixture of suspects and clues. But Cat's curiosity also led her into dangerous waters, for as she closed in on the killer, he moved to stalk her…