The Cuckoo follows Jessica, Nick, and their daughter, Alice, as they relocate to the countryside, hoping to leave financial struggles and family conflicts behind. Taking in a lodger for extra income, Sian charmingly befriends Jessica and Alice, gaining their trust while raising Nick's suspicions.
Dark family secrets surface when Alice discovers the long-hidden truth of her adoption, with Sian revealed as her birth mother. Distraught, Alice runs away with Sian but soon Sian's erratic behaviour begins to frighten her while Jessica and Nick uncover Sian's troubled past.
Jessica and Nick track down the pair, where Jessica fights fiercely to save her child. However, as Alice is returned to her arms, Sian disappears. The family are left scarred but united.
The Cuckoo stars Jill Halfpenny (The Holiday, Waterloo Road), Lee Ingleby (Inspector George Gently, The Long Shadow), Clare Goose (The Coroner) and Freya Hannan-Mills (Whitstable Pearl).