The Last Raven (1990)
It's a case of lucky thirteen as we enter a new decade. The Last Raven is one of Thomas' best in a while, and is my favourite of his books which have appeared in the 1990s.
At the end of the last book, All the Grey Cats, it seemed that Patrick Hyde had been killed on a mission in Afghanistan. We now find out details about that mission and discover that he's alive and not so well. It's been five years since his last appearance in The Bear's Tears, although in the chronology of the novels it's more like one year
The Soviet Union is dying and the hard-liners want the rot stopped. They have made a deal with the CIA of all people to stop Glasnost. Using a stolen British missile launcher elements of the KGB and Red Army shoot down a military transport which is carrying the wife of the Soviet premier. It turns out that she along with her husband were largely responsible for much of the change in Russia.
Hyde witnesses this and has to try to get the proof to London, but he finds himself on the run from his own people and the Americans. Meanwhile in California Aubrey's niece has stumbled onto the opposite end of the same plot involving the destruction of an American airliner. She is also forced to go on the run. Eventually she and Hyde team up and try to gather more evidence.
Any other author would have these two fall in love. However Thomas decided that they'd hate each other. It makes a refreshing change. Be warned that the book doesn't have a happy ending.