The series is based on a harrowing true story about a number of Irish women who went missing in the late 80s and 90s.
When she writes an article on her mother's murder, the killer resurfaces, hinting at a kidnapping. Lisa and Detective David Burkely (Allen Leech) investigate, connecting the killer to the disappearance of a woman called Amy Reynolds.
https://www.channel5.com/show/the-vanishings/season-1/episode-1-288bcc52-98cb-42a1-850c-cb564b51a356
I cant work out if this has already been shown on another channel. It was previously called "The Vanishing Triangle".