Something is rotten in the city of Swirlyshell. Could be the oysters. Mermaids Beattie, Mimi and Zelda are enjoying a summer on land with legs when they receive a strange CRABAGRAM ordering them to return home at once. Some seriously BAD MERMAIDS are on the loose and the girls are the only ones who can stop them. If they’re going to save the day, they’ll need answers. And a clam car. Definitely piranha-print nail polish. Possibly not the talking seahorse. CAN THEY DO IT?