The team assists DI Paul Renick following the assumed suicide of Jamal Al Sham and discover that he was murdered and was a people smuggler, blamed by Varkey Khoury, head of a family of Syrian refugees, for killing his wife. Varkey's 15 year old daughter Akka approaches Nikki for news of her mother, leading to Nikki sheltering her whilst the police haul in another young woman Tamara as a likely killer. At the refuge camp in Calais apparent altruist Yusuf Hamed assists 12 year old Sosa to come to England whilst Kalil Aziz, an associate of Sham, is also murdered and the police and pathologists make a grim discovery in an English forest.

Los patólogos se unen a la policía para retirar los cadáveres de los refugiados que se asfixiaron en el furgón cerrado y encuentran una posible pista en los mensajes de teléfono enviados por las víctimas moribundas. Mientras se sospecha de un agente de aduanas que está a punto de jubilarse por permitir el contrabando de personas, el equipo establece que el culpable tomó dinero de los familiares de los migrantes a quienes luego dejó morir, incluida la madre de Akka. Yusuf rescata a otro grupo de refugiados de un segundo furgón cerrado, escapando con Sosa antes de que llegue la policía, pero la pista real surge a través de una organización benéfica siria a la que el asesino donó el dinero de las víctimas.

When teacher Lucy Chatham is abducted Nikki and Jack help police officers Andy Steemson and Karen Wretzy investigate the circumstances of her disappearance whilst Thomas assists abrasive DS Maureen Steele when ex-addict Tina Lunt is murdered. Doctor's daughter Jessica Timpson saw a car outside her house near the spot where Lucy was taken and her parents Nick and Ellie fear it may belong to Ellie's brother Alec Porter. Tina's death points to criminal boyfriend Wesley Beale whilst Lucy's sister's boyfriend Jasper Lampton is the key suspect when Lucy, his secret lover, is found dead. Forensic evidence suggests that both women were killed by the same man. Then Beale is murdered.

Jasper, un exdrogadicto, es llevado por Steemson por matar a Beale, quien había sido su proveedor, pero luego es liberado mientras Ellie confiesa su miedo a Nick de que Jessica encubra a Alec, a quien él cree que es el asesino. Luego, Clarissa encuentra un vínculo entre Alec y un crimen de hace veinte años en Brighton por el cual fue absuelto. Como resultado, él huye y Ellie se encuentra en peligro por una fuente inesperada antes de que capturen al asesino múltiple.

Lorna Katz's body is pulled from the Thames and DI Heather Ashton hauls in Kieran Vale, the boyfriend Lorna dumped but wanted to get back with. Another suspect is houseboat-dweller Aaron Logan, a boy who dated both Lorna and Ruth Tresize, a girl who disappeared three years earlier. The discovery of Lorna brings her estranged parents Ali and Chris to seek answers from Nikki. Following a clue on Lorna's phone Kieran does some sleuthing of his own, resulting in his murder, whilst Aaron, the prime suspect, goes on the run but is sought out by Ali, who attacks him.

Ali is arrested for stabbing Aaron, who discharges himself from intensive care aided by brother Ben and his wife Sarah. Visiting Ali in custody DI Ashton suggests that Chris killed Ruth and gets an angry response whilst illegal immigrant Stella Duffour is interviewed as the person who reported Lorna's death, resulting in her being threatened. The pathologists pick up on the evidence that sent Kieran to embark upon his fatal mission and locate the spot where Ruth was killed. An unusual discovery by Clarissa is also instrumental in catching the murderer and closing the case.

El esposo de Clarissa, Max, es llevado al Centro Lyell para ayudar a resolver un caso.

El padre de Becky, Stuart, es arrestado después del descubrimiento de imágenes en el teléfono de Frankie de Becky teniendo sexo a regañadientes con ambos chicos muertos. Sin embargo, Clarissa nota que el compañero de piso dedicado de Becky, Paul, los estaba observando furtivamente, aunque no se encuentra su ADN en ninguno de los lugares del crimen y tiene coartada para ambos delitos. Luego, el director Clive Maitland es apuñalado hasta la muerte después de un enfrentamiento con dos exalumnos, aunque su asesinato parece no estar relacionado con los demás. Cuando Max es llamado de nuevo, establece una conexión letal entre dos partes sin una conexión obvia.

When Luisa Herrera, a former intern at the Lyell Centre, is killed in a car-jacking in her native Mexico Nikki arrives for the funeral, only to find that the body in the coffin is not Luisa's. She seeks out Luisa's boss, Dr Eva Vasquez, who runs a charitable hospital, also a centre for a dedicated band who search for families abducted by drug cartels as the police are too afraid to. Luisa was one of that group. Jack flies out to assist Nikki look for her friend, unearthing the bodies of several torture victims but chief suspect El Buitre refuses to give any information even when Nikki withholds his medication. Eva's son Ernesto is also kidnapped and Eva and Nikki, following a tip-off, go to find him. However Jack discovers Eva's car with Eva inside but no Nikki.

Frantic to find Nikki, who has been buried alive, Jack gets a mysterious phone call allowing him to ring Nikki and another call demanding a ransom and the release of cartel member El Buitre but the exchange goes wrong. Helped by Luisa's lover Gustavo Jack is able to locate and free other abductees from their underground prison, including Luisa herself and Eva's son Ernesto but Nikki is not with them. Ultimately Nikki draws on the lessons she learned from former mentor Leo to try and free herself whilst Jack discovers that she has been the victim of a desperate arrangement.