After the shocking finale of Season 3, six months have passed and the team must overcome their grief to tackle a dangerous crime wave. This time, Professor T is well and truly off his game in his lectures and embarks on a new musical pursuit. Romance is very much alive for his mother Adelaide Tempest (De la Tour), and the lines between professional and personal become blurred for therapist Helena Goldberg (Stevenson). Meanwhile, DI Maiya Goswami (Sunetra Sarker) takes charge of the police force with series favorite DS Dan Winters (White) fiercely at her side.