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.

With a duty to deliver every last letter before Christmas, the beloved quartet of post office detectives are working around the clock to redirect Santa's mail just as Oliver runs into his former Sunday school teacher. When they receive an emotional last-minute plea not meant for Saint Nick, but instead written to God, they must delay their own travel plans to make sure one little girl doesn't lose her Christmas joy-something Oliver and Shane are also struggling to find as they each face painful holiday memories. With a little guidance from a mysterious post office volunteer, Jordan, the Postables are more surprised than anyone to discover they've been a part of more than one miracle on this Christmas Eve.