 Marshal W.T. O Niel is assigned to a mining colony on Io, one of Jupiter s moons. During his tenure miners are dying - usually violently. When the marshal investigates he discovers the one thing all the deaths have in common is a lethal amphetamine-type drug, which allows the miners to work continuously for days at a time until they become "burned out" and expire. O Niel follows the trail of the dealers, which leads to the man overseeing the colony. Now O Niel must watch his back at every turn, as those who seek to protect their income begin targeting him...