Heart of the Dragon by Kym Dillon

Molten Passion, Stolen Bliss…
THE JEWEL THIEF
Daya Krane can’t keep her hands to herself. Not where diamonds are concerned. She’s a jewel thief caught stealing from the mafia. With a hitman out to get her and the cops on her tail, a mysterious escape route seems heaven-sent…
A deranged immortal summons Daya to swipe a super-rare red diamond, it’s an offer the klepto can’t refuse. Especially since her other option is death.
THE DRAGON KING
Arken Imyr isn’t another thief after the same jewel like Daya thinks he is. When the alluring mortal infiltrates his keep to steal a treasure he’s sworn to protect, she should die swiftly. Yet, centuries of isolation with no release have made Arken very dangerous.
He is a raging inferno wrapped in flesh, and Daya is his gasoline. Passion like theirs is destined to ignite. While he can quench his lust, he can’t promise love…
…If she steals his Heart, she steals his kingdom.