Fourteen-year-old Marcus Whitmore is devastated when his beloved Grandmother Evelyn dies, leaving him with crushing regret over their last distracted visit together. Three days after her funeral, as his family settles into her Gothic manor, Ravenshollow, Marcus inherits an imposing eighteenth-century grandfather clock that has stood in the sitting room for generations. When the long-silent clock mysteriously begins ticking again, Marcus discovers it possesses an extraordinary power: by touching the symbols carved into its case, he can travel backward through time to visit his grandmother in moments from the past. Overjoyed to have her back, Marcus begins making nightly visits to relive precious memories and finally say all the things he wished he'd said before she died.
What begins as a comforting escape from grief quickly becomes an all-consuming obsession. As Marcus spends more and more time visiting the past, his health deteriorates and his grip on the present weakens. Through visions of his grandmother's own youth, he discovers that his grandmother struggled with the same compulsion, using the clock to visit her own deceased father for forty years, before finally breaking free. Through haunting entries in the family chronicles, Marcus learns that the grandfather clock has been trapping members of his family for over three centuries, feeding on their grief and refusal to let go of the dead. Now Marcus must decide whether to continue his nocturnal visits to a grandmother who can never truly return, or find the strength to face a future without her presence, even if it means destroying the only connection he has left to the person he loved most in the world.