In "Signed, Sealed, Delivered: From the Heart," the beloved POstables Eric Mabius, Kristin Booth, Crystal Lowe and Geoff Gustafson discover a 200-year-old valentine that could change history, while their investigation of a damaged letter leads them to a public figure who could be brought down by its contents. And in the aftermath of Valentine's Day, Oliver, Shane, Norman and Rita are each dealing with heartbreaking circumstances.