SAS : red notice
(Book)

"Deep beneath the Atlantic Ocean, a small army has seized control of a train in the Channel Tunnel, taking 400 passengers hostage. One man stands in their way. Off-duty SAS soldier Tom Buckingham--alone and injured--is the only chance the passengers and crew have of getting out alive. With only a failing cell phone to contact the outside world, he must use all his training to take out the enemy and secure the train. It's one unarmed man against twelve well-equipped soldiers fresh from a civil war. And to make matters worse, someone from his own side is determined that no one will leave that tunnel alive."--Amazon.