"We've got an emergency. The Green Lantern Corps' power rings have been acting strangely and they've traced the problem back to Earth. Problem is, so has the Sinestro Corps. They're throwing down in the Historic District. Talk to the Recruiter in the Police Station there for more." — Oracle
Talk to Green Lantern Recruiter Drisch at the Midtown Police Station in Metropolis (773 xp)
Upon talking to him, he starts to talk but Superman interrupts him over the communicator, turning the mission into War with the Corps.