A Robert Heinlein juvenile (as in fiction) from 1951, Between Planets tells the story of Don, a 19 year old boy trying to reach his parents on Mars after completing his schooling on earth, only to find himself an unwitting courier of a scientific discovery which could mean the end of the war he finds himself in the middle of. Born in freefall on a spaceship between planets, he is a citizen of all planets and none - and finds his loyalties torn.

Typical heinlein themes, typical heinlein plot, though the hero is uncharacteristically ambivalent for a heinlein hero, all in all it's nothing special, but it's heinlein, so it's still pretty good.