Quag Keep (1978)

Sitting alone in a seedy in in the Free City of Greyhawk, Milo Jagon, swordsman, had deep forebodings of impending danger. On his wrist is a strange bracelet made of two metal bands that hold between them miniature, gemset dice, but he has no member of whence the bracelet came of what power it contains. One by one, Milo encounters six strangers of vastly different backgrounds, each having half-memories of belonging to another world, but each wearing a similar bracelet and under a wizard's geas to find and destroy an alien and evil power that is controlling their lives. When the bracelets grow warm, the dice roll and they enter another stage of the game in which they seem pawns. Using as background the complicated and fascinating war games that are now so widely played, Andre Norton, a leading science fiction and fantasy writer, has created a game within a game, played for life-and-death stakes, that sweeps the reader into an extraordinary world of high adventure where the forces of good and evil war incessantly.