Don Harvey has been enjoying a brief stay at a ranch on Earth, when he receives an urgent message from his parents to return immediately to their home on Mars.  As it turns out, war is brewing between forces on Earth and on Mars, which is brought home to him when his Mars-bound ship is boarded by forces from Earth, and Don ends up (along with an amiable dragon), changing to a ship bound for Venus.  Don's adventures and misadventures eventually lead to his return to his home on Mars.

"Not only America's premier writer of speculative fiction, but the greatest writer of such fiction in the world … [Heinlein] remains today as a sort of trademark for all that is finest in American imaginative fiction."  
- Stephen King

"There is no other writer whose work has exhilarated me as often and to such an extent as Heinlein."
- Dean Koontz

"One of the most influential writers in American Literature." 
- The New York Times Book Review

"Heinlein wears imagination as though it were his private suit of clothes." 
- The New York Times

"Heinlein… has the ability to see technologies just around the bend. That, combined with his outstanding skill as a writer and engineer-inventor, produces books that are often years ahead of their time."
- The Philadelphia Inquirer

"One of the grand masters of science fiction."
- The Wall Street Journal

“He rewrote U.S. SF as a whole in his own image. Robert A. Heinlein may have been the all-time most important writer of genre SF.”
- The Science Fiction Encyclopedia

“Heinlein’s work at its best epitomizes the excitement science fiction can generate by exploring the possible future adventures scientific knowledge and technology can open up for humanity.”
- Twentieth Century Science Fiction Writers

“Robert Heinlein, as much as any writer while I was growing up, taught me to argue with the accepted version.”
- Samuel R. Delany

“The word that comes to mind for him is essential. As a writer—eloquent, impassioned, technically innovative—he reshaped science fiction in a way that defined it for every writer who followed him. … He was the most significant science fiction writer since H. G. Wells.”
- Robert Silverberg