 Philip Winchester plays Sergeant Michael Stonebridge , a " by @-@ the @-@ book " Royal Marine and former Special Boat Service ( SBS ) commando , now assigned to Section 20 who is partnered with Scott to help track down a kidnapped Porter . Stonebridge works for Section 20 and is in charge of his team on the ground . Although the character is married to his wife Kerry ( Alexandra Moen ) , he has an affair with colleague Kate Marshall ( played by Birthistle ) . Winchester describes Stonebridge as " dedicated , disciplined , always plays by the rules and often saves the day . Stonebridge directs his energy trying to protecting others , " though as the story unfolds , the audience would see that Stonebridge " is not the knight in shining armour . " 
