Between Planets (1951) – Don Harvey's parents call him from boarding school on Earth, to join them on Mars when war between Earth and its colonies seems imminent. But war comes while he is in transit, and he is dumped on Venus as their Revolution begins. Eventually, he joins the Rebellion and finds that a plastic ring he had been given to deliver to his parents contains the key to winning the Rebellion and establishing independence for Venus and Mars.
For more information on Heinlien's Juveniles (written between 1947 and 1958) see our entry on Robert Heinlein's Rocket Ship Galileo, The Literary Encyclopedia profile by William Patterson, University …
Patterson, William. "Between Planets". The Literary Encyclopedia. First published 10 November 2004
[https://www.litencyc.com/php/sworks.php?rec=true&UID=16610, accessed 16 December 2017.]