Gemma whelan stars in the itv adaptation of kate london's first novel post mortem. A veteran beat cop and teenage girl fall to their deaths from a tower block in south east london, leaving a five year old boy and rookie police officer lizzie griffiths on the roof, only for them to go missing. Detective sergeant sarah collins is drafted in to investigate, working to find lizzie before she comes to serious harm, but also to uncover the truth behind the grisly tower block deaths.   when ds sarah collins and her colleague dc steve bradshaw are called to an incident at portland tower in south east london, they are met by a terrible scene on the ground at the bottom of the tower lie the bodies of long serving police officer, pc hadley matthews, and a 15 year old girl, farah mehenni. When she gets to the roof of the tower sarah finds a five year old boy ben, a rookie police officer, pc lizzie adama, and lizzie’s boss, di kieran shaw.  before sarah can interview lizzie about what exactly happened at the tower, lizzie disappears. The more sarah and steve investigate, the more they realise that key evidence is being withheld, and that their investigation is being subtly undermined. Despite this, step by dogged step, they uncover the incidents that led to the tragedy of the tower, and reveal the fiercely complex moral maze that trapped the characters in the past, and still traps them in the present.