Sirena, Empress of Evil, was the ruler of the Sargasso planetoid. She captured a rocket-plane containing an Earthling test pilot and Kyro to lure Green Lantern to her planet. Kyro manages to escape and he meets up with Green Lantern and points out the "electrono-magna-wave apparatus" she'd been using to pull down ships, which he melts with his ring.
Sirena distracts Green Lantern by sending her bat-like minions to attack him, then once he's distracted she has an owl-like creature knock him out so her minions can steal his ring. With Green Lantern out of the way she plans to attack the Guardians of the Universe with her space fleet.
The Guardians contacted Kyro telepathically and told him where Green Lantern was being held, and with the unexpected help of the owl-like creature, Beepy, distracting the guards; Green Lantern recovers his ring, then flies to Oa and defeats Sirena's space fleet.