Creep from the Deep by R. L. Stine

Age: 7-11

Fright-master R.L. Stine invites you on an all-new, all-terrifying adventure! Billy and his sister, Sheena, unwittingly dive into a terrifying mystery when they accept a surprise invitation to HorrorLand - the amusement park that always lives up to its name. But first Billy and Sheena must sink or swim aboard a doomed ship that happens to be underwater - with a captain who happens to be dead. At least, he used to be!