During the Tiger Cruise, which is intended for family members of the sailors on board, Maddie (played by Jen Lilley) is reporting on the ship and the families on board for her Norfolk newspaper. While on the ship, she meets Lieutenant Billy Jenkins (played by Trevor Donovan), a Navy officer who is dedicated to his job but also has a soft side. Maddie and Billy begin to bond over their shared appreciation for Christmas and their love of the Navy.
However, Maddie soon becomes intrigued by a mystery she discovers in the ship's archive room. She finds an old letter written by a sailor who was on board during World War II, which reveals that a certain crew member was accused of stealing a valuable artifact. Maddie sets out to uncover the truth and with Billy's help, they dive into the ship's past and uncover secrets and hidden dangers that threaten to derail their investigation.
As Maddie and Billy work to solve the mystery, they begin to fall in love. But as they get closer to the truth, they find themselves in danger. Maddie must decide whether to continue pursuing the mystery or to protect herself and those around her. In the end, Maddie uncovers the truth and finds a renewed sense of hope and love in her life. USS Christmas is a heartwarming holiday mystery that highlights the bravery and dedication of those who serve in the Navy.