Scorpio Descending - Alex McDonough

No Time Like The Twentieth Century 

Savage Hunters are tracking the alien known as Scorpio. The chase has crossed two planets and thousands of years, and the Hunters are finally caching up. In a last, desperate gamble, Scorpio flees blindly through time with his only ally, a human girl named Leah. 

Scorpio and Leah find themselves in Russia on the eve of revolution.

Unfortunately, the trip damaged their time-traveling orb-its powers are gone. Stranded, they must find the only person who can help: a brilliant scientist whose mentor was Albert Einstein.

Time is of the essence. Russia is about to explode in the blood and violence of revolution, and nobody is safe. With the Hunters on his tail, Scorpio needs the orb if he's to save his friends, his people-and himself.

Scorpio • Scorpio Rising

Scorpio Descending • Scorpio Dragon's Blood

Scorpio Dragon's Eye • Scorpio Dragon's Claw