Contains spoilers for this episode.
Detective Karin Parke tells an inquiry how an investigation into a journalist's death became a national disaster. Working with Blue Coulson, she finds an artificial bee lodged inside the victim's brain. The insects were built to replace lost pollinators, but someone has gained control of them. A second death points toward an online campaign inviting people to nominate hated figures, with the most mentioned person selected to die.
Karin and Blue try to protect Clara, the next target, in a safe house. The swarm penetrates their defences and kills her. They learn that the insects' surveillance capabilities were part of the government's arrangement with their manufacturer. The investigation leads to Garrett Scholes, who wants to punish the cruelty he sees online. His abandoned equipment offers an apparent opportunity to shut down the system before another nominated victim is attacked.
Blue discovers that the stored list contains everyone who participated in the hashtag campaign. Karin warns that deactivation may trigger the real attack, but Shaun Li presses ahead. The insects restart and kill the campaign's participants in huge numbers. At the inquiry, Karin describes Blue leaving the police and apparently taking her own life. Elsewhere, Garrett watches the proceedings, believing himself safe. Blue is alive and following him abroad. She messages Karin that she has found him, then continues after him through the streets.