Law and order is provided by the International Space Police Force (ISPF), twenty part-time volunteers disparagingly nicknamed the "Star Cops". The decision has been made to put the ISPF on a permanent full-time footing and a new commander, Nathan Spring, has been appointed to accomplish this. Many of the series episodes deal with Spring's efforts to establish the Star Cops—he sets up a base of operations on the Moonbase, recruits new staff, roots out and dismisses corrupt officers and works to extend the Star Cops' reach first into the American space stations and then, at the end of the series, the far-flung reaches of the Mars colonies, all the while investigating whatever crimes occur along the way.