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...