Buck the System by Margaret Madigan

Dr. Melinda Emerson is still reeling after her escape from Russian mafia terrorists. If she never sees or hears anything Russian again, it’ll be too soon. She’s ready to go back to researching a cure for Alzheimer’s and to begin building a life with her new man, Grady “Buck” McCormick. But the Russians aren’t done with her just yet.
Grady “Buck” McCormick likes to be in charge. But he loves Melinda more. Turns out it’s not so easy for a single alpha male to learn how to be a partner rather than a leader, but he’s determined to do it. That resolve is put to the test when his team gets orders for a new mission where the tables are turned and he must relinquish control, depending on Melinda to protect him.

The Russian mafia is back like a bad penny. They’ve been experimenting on the cognitive enhancing drug Melinda invented. Their version makes users obey orders without question, but it’s also fatal. Melinda is sent along as a civilian consultant with two SEAL teams to infiltrate a secret Siberian lab, secure the head scientist, and retrieve all the research on the drug. But the mission goes sideways when Buck and several of the SEALs are injected, and Melinda is forced to find a cure, or lose the man she loves.