Venom: A Dark Enemies to Lovers Mafia Romance (Cruel Saints Series) by Cora J Riley

Maren Cole has one assignment: get inside Aleksei Voss's operation and expose what he's hiding. She gets the job. She doesn't expect the ice-cold security mogul to see straight through her cover from day one — and let her stay regardless. Aleksei doesn't trust easily. He doesn't want easily either, not until a journalist with sharp eyes and a fake résumé walks into his building and refuses to be intimidated. As the line between surveillance and seduction collapses, Maren uncovers a conspiracy bigger than either of them — and a man capable of far more devotion than his reputation suggests. Some men build walls to keep people out. Aleksei built his to keep something terrible contained. Maren is about to find out exactly what.