Study Buddies discussion

Ok so I have only read the Study Series so far. I have all the others but I just finished Fire Study and then moved on to Ice Study. So I read it and the whole thing is great! But then one of the last sentences confused me...
"We had thought those glass prisons were safe and unreachable. And you know what happened to them."
What happened to the glass prisons??! In the Fire Study that I read the last thing to happen with them was Yelena asked Valek to hide them... So they were safe as far as I know. Is the story I'm missing the GLASS SERIES? If someone could help me figure this out it'd be awesome!

Yes, you need to read the Glass Series in order to understand that.

Awesome. Thank You!

I think I'd still put Ice Study after the Glass trilogy. Since it mentions a few characters and events that happen in those books.

Ice study takes place during the Glass series...