PERIDOT: THE CAESAR TALISMAN by Tyree Campbell

Peridot and her two friends continue to battle not just one, but two mobs. One is run by Mad Paul Spirito, a protégé of Mars, the God of War; the other is headed up by a gangster known as The Fist. Meanwhile, Ricia Ryder—Peridot’s alter ego—is now courted by a gendarme; an archeology expert who might be associated with Mars; and a gigolo sent by Spirito. Sequana, the insane Celtic goddess who empowers Peridot, deprives Peridot of those powers in a fit of pique.

And everyone wants the Caesar Talisman, a gold coin with the power to make its owner a master military strategist capable of conquering the world. Caesar had one. So did Genghis Khan, Napoleon, and Pachacuti, among others. Only the one that Caesar possessed remains in existence.

Peridot has it. And everyone wants it.

So what’s a superheroine to do? One thing at a time...
 
In the Peridot series:
Peridot-Three Against the Mob
Peridot - The Caesar Talisman
Peridot - Avatar
Peridot - Balance of Power