The episode begins where the last one left off: the bomb on the bus has just exploded and the NCIS team is dealing with the aftermath of it.
Gibbs spots a young boy at the scene and takes off after him. He loses him.
The terrorist group calls themselves "The Calling". They are recruiting young children via the internet to their group. They are also purchasing S-mines, which are similar to "Bouncing Betty" - a bomb that when triggered shoots up into the air and detonates, providing a shrapnel shower.
Matthew Rousseau is identified as the leader of a cell.
Gibbs meets with Agah Bayar, a Turkish arms dealer who used to work with the DIA and asks him to hunt down the people buying the S-mines.
Ducky and Abby connect the dead teen on the bus to a group of three other teens, all of whom were involved with terrorists in Syria. Two of them are dead, but one still lives: Sarah Goode. Gibbs tells Bishop to bring her in for questioning.
Vance sends Dorneget and McGee to represent NCIS at a think tank in Cairo. They are to meet with GID Officer Hassan.
Vance tells Gibbs the deal with Agah Bayar is off.
Sarah Goode identifies one of the screen names on the chat room list from the last episode. His name is Sadiq Samar.
Bishop discovers a building purchased out of Samar's bank account. She, Gibbs and Tony go to the building to hunt him down. They find a bloody bayonet, and a young boy holding a gun. Gibbs gently takes the gun from him. Bishop takes him into custody.
Gibbs tries to interview the boy - Luke Harris - but he refuses to speak.
Dorneget and McGee learn that Rousseau has been captured and is en route back to the U.S.
Bishop, Abby and Tony investigate a secret room in Samar's house. Abby determines that the room was used to set up a set of connected bombs, as a test.
Gibbs interviews Harris' adoptive parents who tell him that Luke had been visiting a number of sites and talking to people who were bullying him because he's adopted.
Gibbs brings Luke Harris back to his house, to try and reach him. The boy reacts to Gibbs' stories with anger and self-loathing, telling Gibbs to kill him.
Vance briefs Gibbs and Tony about the S-mines. He says as many as six bombs canl be connected via encrypted wifi and tripped by a virtual wire.
Tony outlines a plan to Vance to obtain Bayar's help without giving him a monetary deal: to threaten deportation of his mother unless he assists NCIS. Vance approves the plan, with the caution that they must not get caught.
Bishop and Tony meet with Bayar. He agrees to help.
Gibbs finally gets through to Luke. Luke tells Gibbs he was at the secret room on Samar's orders, and was to shoot as many people as he could once NCIS showed up. He provides the new chat room coordinates.
Abby and Bishop enter the chat room and learn that Samar plans to punish Luke for not carrying through on his orders.
Gibbs takes Luke to his parents' house but notices the door is open. He tells Luke to stay in the car. Gibbs goes in the house and finds Luke's parents both shot dead.
McGee interviews Rousseau and learns that the terrorists have something planned for the other members of the think tank.
McGee phones Dorneget and warns him to evacuate everyone from the hotel.
Dorneget manages to evacuate many people. He spots the laser tripe wire. A man trips it, several S-mines eject from the ground and are detonated. Dorneget is killed.
Bayar gives Tony and Bishop the names of three people seeking S-mines. As they talk, an SUV drives by and shots ring out, some of which hit Bayar.
The NCIS team arrives at the airport to meet Dorneget's body.