During a devastating Christmas Eve snowstorm, John the postman arrives at his last stop, at the steps of the Frost family. Here, he rediscovers a stowaway letter in his mailbag, not for his route. It's a letter from a hospitalized grandfather, to a very special grandson. John feels obligated to make the delivery. His unselfish act of kindness leads him, and then the Frost family, on an unforgettable journey across a seemingly endless track of farmland. Little does John know what he's actually carrying. The lantern he carries becomes a mystery, that guides their way through astonishing events. They finally arrive at the Evans house, where they find themselves before an extremely sick boy, a mother's pain, and the mystical workings of God.