Hundreds of years after civilisation has been destroyed by nuclear war, the Earth is divided between the Trackers of the Amtrak Federation - a community living in vast subterranean cities - and the Mutes, who have evolved to withstand the radiation that has driven their foes underground. A long war for possession of the overground has killed and enslaved many of the Mutes, leaving only the Plainfolk to resist the Federation. And now the Iron Masters - a powerful people living in the traditions of the Samurai - have joined the war.Steve Brickman, a Tracker special agent, has travelled to the land of the mysterious Iron Masters in a bid to rescue his Mute friends, Clearwater and Cadillac. Here he has had to navigate the treacherous feudal politics of Ni-Issan. With the help of his psychic kin-sister Roz, the Federation and Clearwater's summoner magic, the three have just escaped, killing the head of Yama-Shita in the process.Under orders from the Amtrak Federation to betray his friends, Brickman must play a dangerous game in trying to appease both sides, for his loyalties are torn. Brickman's love for Clearwater and respect for Cadillac pull him away from the duty he owes his own home. Still fleeing and ruthlessly pursued by the Iron Masters seeking revenge, they must also avoid the 'aid' of the Federation agents who would use Cadillac and Clearwater for their own ends.Blood River, first published in 1988, is the fourth instalment of Patrick Tilley's internationally best selling science fiction epic, The Amtrak Wars Saga.