Training for Revenge by Brenda Cothern

Anthony Mancini, Chicago’s Italian kingpin, has no choice but to bring in outside help to train his niece, Valentina Russo who is hell bent on exacting her revenge on the Irish mob that had her abducted and abused her four months ago.
Mancini hires two assassins to do the job. Gordon Wellington is a hands-on, up close, silent killer. Craig Barlow prefers the distance poisons allow to take out his marks.
Years of beating each other to take out the same marks has built an unrivaled hatred between them. Hatred or not, now they have the same contract: Train Valentina Russo. Working together was never part of their plan. Neither was a relationship.