Sirena, ruler of the Sargasso planetoid, captures a rocket-plane containing an Earthling test pilot and Kyro to lure Green Lantern to her planet. Kyro manages to escape 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 contact Kyro telepathically and tell him where Green Lantern is being held, and with the (inexplicable) help of the owl creature, Beepy, distracting the guards Green Lantern recovers his ring, then flies to Oa and defeats Sirena's space fleet.
Green Lantern's powers work perfectly against the yellow bat-creatures and spaceships utilized by Sirena against him, despite his ring's weakness to the color yellow.