On the first morning of summer, Pip ran down to the beach and almost tripped over her dog Biscuit. He had a green bottle in his jaws, washed up between two rocks. Pip pried it open. Inside was a paper torn down the middle: half a coastline in faded blue ink, and one word left at the rip. It said HARBOR.

Pip studied the faded ink instead of rushing off. The half-coastline matched the bay in front of her, but it showed a small cove that wasn't on any modern map. She decided to follow the inked shoreline on foot, hugging the rocks, to find the cove the mapmaker drew.

Pip and Biscuit picked their way over slippery rocks until the shore curved into a hidden cove, just like the ink showed. Tucked in the back was a small sea cave, its mouth half-covered by the rising tide. The water was creeping higher by the minute.