Mithril and the SRT rescue refugees caught in a civil war in the African country of Balic. However, during the fighting, they discover that the enemy possesses advanced weaponry rivaling their own. They surmise that a highly funded, well-equipped organization may be supplying their enemies.

In Nanjing, Amalgam kidnaps peace delegations from Northern and Southern China and fortify themselves in an underground tunnel beneath the Yangtze River. Mithril attempts a rescue in the tunnel's dangerous confines, but falls into Amalgam's trap.

Mithril is perplexed at how the enemy is able to follow their movements. Once they realize that their communications have been compromised, Tessa and Commander Andrei Kalinin give false orders to facilitate the rescue and turn the tables on Amalgam.

The SRT travels to Sicily to capture the traitor from the Nanjing operation. Sousuke has difficulties balancing work and school when he tries to have a phone conversation with Kaname and to drive a getaway vehicle at the same time. A mysterious AS also appears to help the team get away. Seeing the stress of his everyday duties, Mao decides to ask Sousuke about his own plans for the future.

Mithril attempts to learn more about the mysterious Amalgam organization. Sousuke and Kaname's relationship begins to blossom; however, the Mithril leadership forbids him from seeing her after his bodyguard duties are assigned to another agent.

Sousuke argues with his replacement, Agent Wraith, about the mission to protect Kaname. Kaname wonders why Sousuke has not been attending classes in days and starts to become worried. When she needs to see him after a chance encounter with Amalgam agent Xia Yu Lan, she finds his apartment vacant and he has disappeared.

After Sousuke arrives back at Merida Island, Tessa berates him for emotionally involving himself with Kaname and neglecting his other duties. Lt Belfangan Clouseau, the pilot of the AS seen in the Sicily operation, transfers to the SRT as its new commander. After he clashes with Kurz at the bar upon offending the memory of the SRT's dead comrades, Clouseau stages an AS duel to help Sousuke properly operate the Arbalest.

Kaname confronts Agent Wraith about Sousuke's departure, but as she is about to get answers, Xia Yu Lan ambushes the two. Kaname outwits her pursuer until Leonard Testarossa, another Amalgam agent who is also Tessa's brother, shows up and kills Xia Yu Lan. He reveals that the assassin was a rogue agent acting outside of Amalgam's interests.

Xia Yu Lan's twin sister, Yu Fan, hijacks a Venom AS to become an agent provocateur between the Northern and Southern Chinese Army units in Hong Kong. Sousuke and Melissa are deployed by Gavin Hunter to the area in a team of SRT/PRT personnel of East Asian origin to find the AS, but his feelings for Kaname nearly places the Mithril reconnaissance force in danger. After a tough sermon from Melissa touches a raw nerve, Sousuke deserts the team.

Sousuke continues to wander in Hong Kong and encounters a prostitute who looks very much like Kaname. Tessa is "forced" by Admiral Jerome Borda to deploy Clouseau, Melissa, and Kurz to the island after sightings of the Venom AS are confirmed.

Xia Yu Fan leads Sousuke to Gauron while she runs off to fight Clouseau, Melissa, and Kurz in Hong Kong as Northern and Southern China teeter on the brink of hostilities. Now crippled and about to die, Gauron explains the truth about Amalgam and taunts Sousuke by claiming to have killed Kaname because it changed him into someone weak. Enraged, Sousuke kills Gauron and gets out of the building just as a bomb under his bed explodes. Gates and his Amalgam team also arrive to kill Xia Yu Fan. Tessa launches the Arbalest despite Mithril's orders not to.

Still demoralized by Gauron's claims of killing Kaname, Sousuke still refuses to function until Kaname finally appears to get him back on his feet. Inspired by her presence, Sousuke pilots the Arbalest again to destroy Gates and his men. Kaname returns home to Japan. Sousuke faces the Mithril command, which grants his request to stay with Kaname even if his wages are reduced.