Sometime before the battle on Zorken Island, there was another battle the Bennet siblings got into. It happened on Pierson Island, but that was mostly accidental. At least, that was what Atlas and Hugo said.
It was because Slater and Benjamin, Zoren's assistant, got abducted. Or rather, they were taken into the enemy base because of the trouble they got themselves into. So, the siblings did what they had to do — go crazy.
What they uncovered was an illegal gambling ring that forced people into what was practically modern slavery.
Of course, they managed to get out of there alive and even got the syndicate arrested.
But during that time, Penny almost got herself killed. From what Atlas and Hugo told Lola, it was because Penny thought she was helping a child. As it turned out, that child injected her with something that incapacitated her.
