The pendulum clock at the top of the lighthouse strikes thirteen at midnight, and its count wheel only has twelve notches.
Marlow Vance repairs antique clocks and has not stayed anywhere longer than a few months since he was nineteen. The town council hires him to pull the movement out of the Greywick Point lighthouse and crate it. On his first day he reads the maker's mark and recognizes it — the same make, the same year as the one his father left under a tarp and never finished. He decides not to tell anyone what he intends to do about that.
Idris Calloway keeps the light. He has kept it alone for eight years, he sorts his keys so somebody else could find them in the dark, and he has learned to send people off before they can leave on their own.
That night the clock strikes wrong for the first time. According to the woman who runs the tea shop, it does that when somebody under the roof starts keeping a truth from himself — and it will only ask three times before it takes something.
Two strikes are already gone. Neither man will say the thing he is holding.