R.R. Winterbotham 
The Thought-Feeders [EPUB ebook] 

Captain Lewis Hawes and Dr. Kempster Duerkes find themselves trapped in the stratosphere by mysterious green clouds. In a realm where thoughts become real and the impossible becomes possible, the line between reality and fantasy blurs. As they uncover the secrets of this strange new world, they must use their minds to survive.

With the help of the beautiful Loetta, they discover the true power of imagination. But can they harness their thoughts to escape back to Earth before it’s too late?