Ronan & Finola is a children's book about a mermaid boy named Ronan, and his best friend, a little girl named Finola who lives in a lighthouse near the ocean.  Ronan runs away from the other mermaids because he looks different, but finds a friend in Finola, who appears not to notice his strange blotchy skin.  When the lighthouse is destroyed in a storm, they realize Ronan might be able to help, and discover he's different in the best sort of way.