When Mike Gabrieli's neer'do'well brother Tom disappears shortly after discovering a fabulously valuable Aztec relic, Mike rightly suspects that this time the family's black sheep has got himself into the kind of trouble from which even Mike won't be able to extricate him. But still, Tim is -- or was -- his brother, and Mike must do what he can.
For Mike this is the beginning of an adventure beyond imagining, an adventure that will put him in constant peril of his life as he shuttles between past, present and future of an alternate reality, fighting beside the descendants of the Incas as they battle to erase Pizarro's bloody footprints from the New World, and secure the reality of their own existence.

But is the "alternate reality" really an alternate, or is Mike actually struggling to erase the very future that gave him birth? The answer lies in the source of all his troubles and his only hope of survival: THE MASK OF THE SUN

--From the ACE Cover blurb.

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It is an ancient Aztec mask, worth a fortune in fold, but it holds more power than the human mind can comprehend. Tom Gabrieli has dredged it from the sea and vanished. Mike Gabrieli dared to wear it and his life will never be the same. Suddenly he is the focal point of an inconceivable war between time-traveling Tenokas and 16th century Incas. But more than his life is at stake; the total dissolution of history as we know it will be the price for his failure. The key to victory is an unimaginably awesome weapon from the future, and the only man who can defeat Mike Gabrieli also wears THE MASK OF THE SUN.

--- From the TOR Cover blurb.