The ninth turn
After Blip's talk with Quinn, he knew something was up. He was doing his own little investigation into what had happened that day. He saw that she had no injuries coming back from the fight with the emperor tier beast. That on its own was strange.
Yes, Quinn was with them with his great strength, but even he looked to be hurt along with the rest. What tipped him off the most was that Fex had told his own tail of events. He knew if anyone was going to crack, it would be him.
Blip had questioned everyone that day what happened, and most of them gave vague answers based on the information that everyone already knew.
When asking what happened, Fex had made up a complete lie that didn't fit with what the others had said, yet he was clearly there.
"Stop worrying about your sister," Dennis said, punching him on the arm. "She's strong; in some cases, I think stronger than you."