Henry Kuttner 
Time Axis 

Called to the end of time by a being they knew only as The Face of Ea, four adventurers from the twentieth century faced a power that not even the super-science of that era could meet — the nekron, negative matter, negative force, ultimate destruction for everything it touched. It seemed hopeless to expect them to win this battle for the fate of the universe — but between them they had a power they themselves could not suspect.