It returns six months after the shocking finale of Season 3, and the team must overcome their grief to tackle a dangerous crime wave. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?　　This time, the gloves are well and truly off for Professor T in his lectures and 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.