The main theme of The Mark can evoke apocalyptic associations. In the game, we are dealing with an alliance between the Al-Qaeda terrorist organization and the Russian multi-millionaire Ilya Raków. Both sides have one thing in common - they are not supporters of Western culture and influence. One of their main resolutions is the razing of London. They want to achieve their goal by using nuclear warheads, the devastating action of which would paralyze the entire region.

Two men stand in opposition to the antagonist forces - Steve "Fletch" Fletcher, who is an officer in the Marines; and Austin Hawke, a mercenary paid by a Russian billionaire. Each player chooses one of the above two heroes before starting the game. Sometimes they work as a duo, but most of the missions must be performed individually. Each of them has completely different weapons. Austin Hawke's set seems to be more qualified and better, but Steve Fletcher, due to his internship in the Marines, is a better athletic and agile person than his partner in the fight against Al Qaeda and Ilya Rakov.