Not entirely accurate, or whatever, but this is a pure cliffhanger moment in Watchmen. It completely turns the status quo of traditional books on their heads - Usually, the good guys learn of the bad guy's plan, and go to stop him with minutes to spare.

Here, the bad guy is one of them, and not only does he enact his plan, he does it nearly a whole hour before they arrive, and actually succeeds with no chance of them changing the course of what he's done.