Not as we know it

Twins Jamie and Ned do everything together, from watching their favorite show, Star Trek, to riding their bikes, to beachcombing after a storm. But Ned is sick with cystic fibrosis, and he may someday leave Jamie behind. One day the boys find a strange animal on the beach: smooth flesh on one end, scales at the other, and short arms and legs with long webbed fingers and toes. Could it be a merman, like in the old stories Granddad tells?