Captured by his own former Corps members, Sinestro is thrown into a cell meant to force him to drain the remaining charge from his ring. He finds himself with a ridiculous number of captured Korugarians that are all very, and rightfully, pissed at the former renegade Lantern. Hal suggests that he make more rings, empower them, and then use that window of having a Green Lantern powered army to take down the Sinestro Corps.
It’s not a bad idea in theory, Sinestro makes dozens of rings, dozens of temporary Green Lantern’s that have enough power for maybe ten minutes of juice.
However, they all hate him and immediately turn the power against him, treating the Green light as one of vengeance against their former oppressor turned hero.
Whoops.