British undercover agent Harry Brown is sent to Northern Ireland to infiltrate the IRA to find (and terminate) the assassin of a British Cabinet Minister. Harry is alone, the army hasn't been told he is being put in place, his wife is fed up with him and his job, and his sole new friend, an Irish woman who falls for him, will be consumed by his relentless search for the assassin.
After the IRA shoot down a cabinet minister in front of his London home, the government send SAS man Harry Brown undercover to Dublin to track down the killer against the advice of the army and intelligence.
While Harry begins a relationship with a local girl, the Special Branch launch their own investigation, which leads to a young woman's suicide. The IRA learn about Harry via a careless remark made by Colonel Frost in a restaurant.
Harry learns the identity of the assassin, but with the IRA on his tail, targeting all of his known associates, he finds it hard to complete his mission.
