In southeast London, a young mother has been accused of the unthinkable: poisoning her own child. Then, as he recovers in hospital, someone tampers with his IV line and leaves him to bleed to death. The mother, Ellie, denies all charges and criminal defense lawyer Sarah Kellerman takes on the case. But even as Sarah begins to believe her client, something about her story doesn't add up. And if Ellie didn't harm her child, then who did? Balancing the case with raising her disabled five-year-old son, Sarah becomes more and more involved, overstepping professional boundaries in an attempt to uncover the truth. The hospital refuses to give answers and a key witness disappears, but it's only when her own son becomes unwell that Sarah realizes she's been drawn into a dangerous and deadly game.