The Message (Animorphs #4)

The wildly popular series by K.A. Applegate is back! It all started with the dreams. But Cassie didnt pay much attention to them. She and her friends have been having nightmares ever since they acquired the power to morph. But when Cassie discovers that Tobias has been having dreams too – the exact same dreams – about the ocean and a voice thats calling to them for help she decides its time to start listening. Now she and the others have to figure out if the dreams are a message or a trap.