The McNasty pirate twins, Captain Gruesome and his brother, Captain Grisly, are determined to get their grubby hands on the treasure buried in the sleepy seaside village of Little Snoring. But the McNastys discover that two clever young friends, Tat and Hetty, are equally determined to find the treasure, and soon they are all embroiled in a rollicking test of wits to see which pair will prevail.