Frank Endicott is a professional worrier. He worries about everything from lions and black holes to submarines and armadillos, carefully listing his fears alphabetically in a notebook. Even the cheerful neighborhood pig, Mercy Watson, cannot distract him from his vivid nightmares. But Frank's worries take a very real turn when he accompanies his neighbor, Eugenia Lincoln, to a dark and dusty thrift shop to duplicate a key. The odd shop owner accidentally sends them home with a mysterious third key! Now, Frank is faced with a genuine mystery that sends his dread skyrocketing. What does the extra key open? Can he solve the puzzle without letting his fears completely take over? With a little help from his friends, some warm hot cocoa, and the comfort of classic stories read aloud, Frank might just find the bravery he needs. This endearing and funny tale is a perfect balm for anyone who struggles with the unknown.