Henry Kuttner 
Time Axis [EPUB ebook] 

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.