Fever is the second book in the Chemical Garden Trilogy by Lauren DeStefano. I loved Wither and I loved this one, even though it is fairly different.
The major difference is that it is more action-filled, like Pandemonium was more action-filled than Delirium. Both Pan and Fever were more Hunger Gamey than the first books in their respective trilogies.
No matter, I loved Fever, every bit of it. There were surprises that make me gasp, it is very unpredictable.
If you remember from the end of Wither, Rhine and Gabe have escaped the mansion and now are trying to make their way back to Manhattan to find Rhine's twin brother, Rowan. That creepy Vaughan just doesn't let up though. And Gabe and Rhine end up in some pretty miserable places, making them wonder if they ever should have left. I found myself not liking Gabe very much. He seemed kinda pouty and wimpy, or maybe it's just that Rhine is so strong.