Left alone for the first time on the island he calls home, Simon is looking forward to a day of personal indulgence. His sister Ellen only wants to make sure they get their chores done. Their parents are busy trying to convince the government not to close the lighthouse that the family operates, and it's up to the kids to make sure everything runs smoothly. Neither Simon nor Ellen is prepared for the mysterious and potentially dangerous visitor who brings with him an unexpected storm and a riddle that may lead to treasure-treasure that could help them save the lighthouse. Simon and Ellen have to work together to solve the riddle before the stranger-or the weather-destroys their chances.