On the same day that a terrorist attack brings London to a standstill, general practioner Dr. Mona Harcourt receives the devastating news that her brother, Dr. Kareem Shirani, has been kidnapped on his way home to the UK from his charity clinic in Lahore, India.

Having secretly got in touch with Danny in Lahore, Mona is approached by police counter terrorism chief Vivien Barnes to travel to Pakistan and identify Kareem's body. Despite her husband Guy's resistance, Mona immediately flies out and tries to make contact with her nephew. But when she absconds from a Lahore mortuary to attend a rendezvous with Danny, the Mona's search leads her to a remote part of the city and grave danger.

Mona returns to the UK and is determined to investigate Danny's suspected links to radical Islam despite her injuries. But her efforts to get Danny to safety on the day of Kareem's funeral have unexpectedly dire consequences for the family.

Mona is released from custody and agrees to become a tasked witness, promising to help the police bring Danny in as an informant. But the fallout from her actions at home is disastrous, and her marriage is under more strain than ever.

Omar attempts to step in and rescue Danny but puts the entire counter-terrorism operation in danger. With the terror cell compromised and off-grid, the police's trust in Danny is severely damaged in the process.

With his client Mr. Khalid now in police custody, Guy is forced into a difficult decision about his own loyalties, whilst Danny and Hamoud await instructions about the target of the planned attack. A shell-shocked Mona is reunited with her loved ones and attempts to put the pieces of her family back together again. However, Barnes and the counter terrorism police face a desperate race against time to stop more attacks on London and save Danny before it's too late.