It was about a boy who went into some other realm with his brother (I think), his brother got ill or was wounded there and was now dying in the real world. The brother had to go back to the other realm to save him. I seem to remember that he went back with a girl and they rode on lily pads at some point. There were weird black flying things that were trying to get them.
Not much to go on I know but I am trying to remember it so that I can get it for my daughter.