In a sea of police dramas, Four Lives (BBC One) stands out. That’s because the police are the villains, rather than the heroes. It is a true-life drama about the botched investigation into Stephen Port, a serial killer who murdered four young men between 2014 and 2015.

Of course, Port is the evildoer, played with chilling banality by Stephen Merchant. But he is not the focus. The story being told here is of the victims, and how justice was served only because their families and friends were determined to uncover truths that the police made no effort to find. This is not a flight of dramatic fancy by the programme-makers. Last month, an inquest jury ruled that failings by the Metropolitan Police probably contributed to the deaths of the last three victims.

Four Lives begins a day after ITV’s drama series Anne, and there are parallels. Both focus on a grieving mother fighting for justice for her son: Maxine Peake as the mother of a teenage boy killed at the Hillsborough Disaster in Anne, and Sheridan Smith here as the mother of Anthony Walgate, Port’s first victim.

Smith’s grief, as Sarah, is a complex thing. It unfolds over the three episodes: we see her bewildered, numb, angry, bereft. Her behaviour does not always make her likeable. Smith brings a humanity and a realness to the role that few other actresses could match.