Red Strike: A Strike Back Novel (4) by Chris Ryan
Book 4 in the Strikeback Series
A former Russian spy, living in hiding in Malta, goes on the run after an attempt on his life. He's been targeted because of what he knows about chemical weapons and the poisoning of an exiled oligarch who cut a deal with MI6, but he's actually got information about a planned Russian invasion.
Now he's gone to ground, and MI6 want to get hold of him before the Russians do.
When a retired general learns about the op he reports back to his Russian paymasters. The former spy must be killed before he spills his guts to MI6. The General has an ex-SAS member on his team who is blackmailed into executing the Russian spy once they find him. But the operation goes wrong, and series hero John Porter escapes with the spy. John Bald and the ex-SAS villain must work together to track them down before it's too late, and expose the General before it's too late and Russia reconquers the Baltic states...