Martin is a young man who makes his living selling stolen items. He is recruited by both the IRA to fight the British and by the British to spy on the IRA. He initially gets involved at a low level in order to get things like a good job, an income, a car, and a girl. The movie has some personal aspects as well. Some lines include, "Your Irish. You are born with an opinion." Or when his mom finds out Martin's gf is pregnant, "You'll do the right thing, or I'll kill you myself."
Martin's gf, the mother of his son, and expecting again, has different priorities. Apparently living and raising a family is more important than keeping Ireland from being British. As Martin watches people die and get tortured around him, he re-examines his situation and realizes he is in too deep and wants out.
Martin's wife/gf and mother are the only real likable characters in the story. Everyone else is caught up in causes and killing. The basic theme of "the end justify the means" is tested throughout as Martin questions the deeds of both sides.
Interesting, but Irish is not English. I used the subtitles.