The Orlov Diamond

The average life expectancy of a treasure hunter is two years...
Washed up mixed-martial-artist, Jonathan Lloyd, is after a career change. His lecturer, Simon Ladbrook, is an ex-treasure hunter trying to escape his past.
Ladbrook introduces Lloyd to the D&E, a dangerous stock exchange for treasure hunters loaded with ex-special forces, assassins, criminals, top sportsmen, and whoever else is willing to put it all on the line.
When the Orlov diamond is stolen from the Kremlin, Ladbrook takes Lloyd into secret tunnels beneath Moscow. For Lloyd, what should have been a straightforward introduction to the world of treasure hunting becomes a deadly game with treachery at every turn.