Dan Bowker comes home from work in a drunken state to discover his teenage son hasn't come home and no-one knows where he is. Meanwhile, Jon Allerton, a trauma surgeon, is at home celebrating his birthday.

Dan and Susie's relationship is on the rocks as he becomes obsessed with Jon and learning exactly what happened the night his son died.

Dan goes to extremes to get Jon to tell him what really happened when Alex died. Jon is confronted with a man so grief-stricken that he might not stop before he's extracted the ultimate revenge.

In episode 4 - a trauma of a different kind. We meet father of two John Walsh on the morning of a crucial operation to remove extremely rare tumors from his spine. Forty people around the world have been diagnosed with the type of tumors that John has, and of them John is the only remaining survivor.