A while before Fex and Quinn had arrived at the shelter. All the students from the other classes had been told to return to the shelter as well. This was an order issued by Fay. Frequently, both Fay and Leo were being called out to help the other groups, it was clear that this wasn't a Green portal planet. Or at least not one that the first year students could handle.
After Leo had gone after Del's class and took longer than usual to return, Fay had decided to make the executive decision to call back all of the students to the shelter. The mission was an important one, and she knew her superiors wouldn't accept this as an excuse, especially after just one day.
Instead, to minimize the risk, the plan was to go as one large group while both Fay and Leo would guide them. Rather than split them up via their homeroom classes.
They would cover less ground this way, and the expedition would be a lot slower, but it also would be safer this way.
