So, it's the climax of "No Good Deed...", the Culties are performing their ceremony, everything's going well.
Suddenly Porter, one of the Culties, breaks out of the ceremony and opens fire on the leader of The Organization.
He and the Reverend Smythe hatched a plan to usurp the power of the ceremony for themselves, so Smythe volunteered to be the sacrifice so he could get close to the leader, not realizing that he would be chained to an obelisk.
Their back-up plan? Porter tries to blow away the Cult Leader himself. And all hell breaks loose.
Much to the consternation of the Investigators who thought they were staging an ambush at the same time. "We declare combat!" (Old rules)
"Get in line, they're already in combat."
(Indignant) "With who?? They can't see us!"
"With each other."