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.