Sauntering through the bulk of the film like a mellowed-out Liam Gallagher, Ifans' valley boyo is first introduced to the joy of drugs at Oxford by the girl who would become his first wife.
After a boring period of marriage, teaching and abstinence, Marks regains his smokin' mojo while driving a carload of hash back from Germany as a favour to an Oxford pal.
Hooked on the thrill, he's soon setting up a major import business from Pakistan to the UK via Ireland, facilitated by IRA loose cannon McCann (Thewlis).
Their allegiance draws the attention of another Oxford alumnus (Christian McKay), an MI6 spook who presses Marks into a little espionage. In return, he's given more than enough leeway to expand his operation to America and beyond.
But while he enjoys his time in the sun, other authorities are closing in. And inevitably, it all starts to go Pete Tong.