When human remains are found by a highway near London, Cassie and Sunny are called in. Dogged work leads the team to a sixteen-year-old girl who went missing on the eve of the millennium. A close-knit group of old school friends hold the key to what happened. Is one of them capable of murder? Cassie is determined to correct the mistakes made in the original investigation no matter the personal cost.

Title from container. DVD release of episodes originally broadcast on television in 2018. Wide screen (16x9). Special features: What is unforgotton? ; Opening scene ; The role of social media ; Locations ; The suspects.