Hoping to celebrate their relationship, Kara and Kyle visit a secluded bridge where couples leave padlocks as symbols of everlasting love.

There they encounter a mysterious woman who warns them of Mary Baxter, a heartbroken bride-to-be whose betrayal and tragic death transformed her into a relentless guardian of true commitment.

Dismissing the legend as nothing more than a ghost story, the couple declares their devotion and seals their promise with matching locks. But when Mary Baxter appears to test the sincerity of their hearts, the lovers discover that vows made without absolute truth carry a deadly price, proving that some commitments are forever.