The story of a quirky quartet of civil servants in the Dead Letter Office who transform themselves into an elite team of lost-mail detectives. Their 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. The intrepid team is led by the charming and idiosyncratic Oliver, who still considers the stamped and mailed letter to be the gold standard of human communication. His two hapless sidekicks are thrown for a loop when a beautiful, no-nonsense technophile named Shane is mistakenly transferred to their inner sanctum and inspires the lovable crew to step up in a risky and unorthodox way.
Oliver leads the postal detective team in investigating a letter from ten-year-old boy alerting his grandmother he’s running away after they've been mysteriously separated. Meanwhile, the rest of the Dead Letter Office team Shane, Rita and Norman is preparing for the arrival of a new supervisor, the larger-than-life Theresa Capodiamonte, who challenges them to take greater risks to deliver the seemingly undeliverable letters and packages. With Theresa's support, they unravel clues that reveal the boy's life is in danger, and they go the extra mile to find the intended recipient of his letter. Back at the office, Theresa prepares to take a risk of her own, as she realizes she has a lifelong dream she’s never pursued and makes her first dance steps in that direction.
After Oliver, Shane, Rita and Norman retrieve a mangled letter addressed “To Whom It May Concern,” their investigation hits a roadblock with an old postmark and a government form for the U.S. Army Office. The accompanying letter from a young woman describes her search for a soldier who saved her life and helped her escape Afghanistan during the war. When they discover the Army officer has gone off the grid, Supervisor Theresa Capodiamonte challenges them to find the intended recipient, even if he doesn’t want to be found. Their search leads them to discover the heart breaking story of a war hero, who not only came home to less than a hero’s welcome, but become homeless and racked with guilt. Ultimately, the team’s attempt to deliver an orphan’s letter to the war hero changes his life while Theresa’s pursuit of her life’s purpose inspires theirs.
When the Postal Detectives Oliver, Shane, Rita and Norman discover an undeliverable love letter, their investigation initially unravels more questions than answers. As their new Supervisor Cora Brandt implements stricter policies and procedures, the team’s challenges are multiplied. In the letter, ranch owner Sam has written his childhood sweetheart with a passionate plea. But the Postables recognize a domino effect this long lost letter will have on its recipient and the people in her life. After identifying an unexpected twist, the Postables simultaneously discover clues amongst their co-workers that shed light on the case.
The past catches up with the postal detectives when Oliver leads Shane, Rita, and Norman on the investigation of a package from a son to his estranged father. The team leaves strict new supervisor Cora behind as they race against time to track down the father before it's too late. But when Shane stumbles onto a clue that decodes the package’s true meaning, the Postables discover a tragedy that changes everything. Meanwhile, Cora has a surprising change of heart that inspires the team.
The Dead Letter Office detectives are dealt their most heart-wrenching challenge yet when they receive an unusual package with a letter from a deceased woman. Rita, Oliver, Shane, and Norman help the family on a dramatic journey to piece together clues from their past, so they can move towards a better future.
When the postal detectives discover a letter postmarked with a future date, it sets off a chain reaction that leads them down a surprising, emotional journey. As Rita prepares for the Miss Special Delivery pageant—and faces threats from Glynis Rucker, an intimidating supervisor whose daughter is also competing for the crown—Oliver, Shane and Norman find themselves in the middle of a unique couple's struggle for acceptance.
Oliver, Shane, Rita and Norman track down a wildly talented but anonymous singer/songwriter using only the lyrics of his undiscovered song, taking on an investigation like no other. As the team follows the song’s clues, they quickly unravel the details of a fated night, where two lives were changed. Meanwhile, an old friend of Shane's arrives and stirs things up in the DLO.
The team at the Dead Letter Office solve clues to deliver not only a letter, but an unspeakable truth that has been buried for years. With special approval from visiting supervisor Rebecca Starkwell, Oliver, Shane, Rita and Norman race to intervene when one man receives devastating news that could lead him to make an irreversible mistake. On a mission to stop him, the Postables’ investigation leads them to another stunning revelation that quickly becomes a matter of life or death.
Oliver and Shane investigate an unusual case that leads them to a bank vault. As Rita prepares for the statewide Miss Special Delivery competition with Norman’s guidance, Oliver and Shane discover they're locked in the vault without enough air to survive. There, they unearth a timeless treasure that will change lives if they don't lose their own.
Norman meets his grandmother for the first time. Meanwhile, the postal detectives try to reunite an estranged family.