The aliens meet an enemy far deadlier than Harrison and the team when Katara, the Angel of Death, comes to Earth. An android from the planet Qar'To, Katara identifies aliens by their special aura, interrogates them about the location of the Advocacy and unceremoniously eliminates them.
When the team begins receiving reports of dozens of alien executions, they are baffled -- who or what could be behind the sudden rash of killings? Visiting the scene of one of the massacres, Harrison ascertains that the method used to terminate the aliens resembles a mini-nuclear bomb, leading him to conclude that new aliens have arrived on Earth.
Determined to learn more about them, Harrison and Ironhorse set a trap to capture several of the new invaders. But the plan is foiled when the aliens arrive at the location and Katara unexpectedly appears to annihilate them. Surprisingly, she doesn't harm anyone on the team, though she does take Ironhorse hostage. However, before one of the alien survivors escapes, he photographs Suzanne and mistakenly identifies her as the android assassin to the Advocacy.
Believing that Ironhorse is dead, the team begins evacuating their secret headquarters. In reality, Ironhorse is being questioned by Katara, who probes his mind and convinces him that she is his friend. She tells him that her race, like mankind, is in danger of being destroyed by the aliens. Her goal is to preserve both Qar'To and Earth by terminating all aliens.
To the team's relief, Ironhorse returns to headquarters unharmed and tells tham all about Katara. After extensive questioning and discussion, the team sets off to meet with the powerful android and forge an alliance.
Meanwhile, the aliens follow Suzanne to Katara's hideout and open fire, mortally wounding Suzanne and Norton. Although disabled in the ensuing battle, Katara is able to destroy the alien strike force with the help of Ironhorse and Harrison. Summoning up her mystical powers, she is able to bring Suzanne and Norton back from the brink of death.
Weakened by the attack, Katara bids a fond farewell to the team. She vows to return in the near future with reinforcements from her planet, and urges Harrison and his people to continue the battle against their common enemy.