Kingpin's Foxglove (The Tarkhanov Empire 1 ) by Bree Porter

She needs to find the antidote...but there is no cure for love. After a year of marriage, Elena Falcone suddenly finds herself a widow and at the mercy of Konstantin Tarkhanov, Pakhan of the Tarkhanov Bratva. Determined never to return to her hometown, Elena makes a deal with the Heal a sick woman and be granted her freedom...or fail and be returned to her family.

Konstantin Tarkhanov has done whatever it takes to build his empire. Now the king of Staten Island, his power has never been greater. But one more obstacle lies ahead of him before he has everything he wants-the wild and intelligent Elena Falcone. Caught up in a complex plot in the world of poisons and gangsters, Elena and Konstantin must overcome many adversaries all whilst dealing with the undeniable connection they share. But not everybody can be trusted and sometimes even those you love are not who they seem.