A group of postal detectives work to solve the mysteries behind undeliverable letters and packages from the past, delivering them when they are needed most.

Tech-savvy Shane joins traditional mail enthusiast Oliver and his small team in the Dead Letters Office, a group of postal detectives whose determination to deliver the seemingly undeliverable takes them out of the post office into an unpredictable world where letters and packages from the past save lives, solve crimes, reunite old loves and change futures by arriving late but always miraculously on time. This motley crew investigates a lost love letter from a sick woman, growing deeply invested in her love story in so doing. When the search leads the team to a falsely imprisoned man, they realize that both love and a man's life are at stake. Taking their investigation outside the boundaries of the postal system, the Dead Letters Office works to clear the name of the wrongfully accused man and reunite him with the love of his life.—Hallmark Channel