Every year on November 5 the English mark the discovery of the Gunpowder Plot in London in 1605 with bonfires and fireworks. It is often called Guy Fawkes Day because many people believe - erroneously - that the plot was devised by Guy Fawkes.

However, while Fawkes played a pivotal role, the man who dreamed up the plot and was its driving force was Robert Catesby (Harington), a 30-year old Warwickshire gentleman.

Catesby is a committed Catholic at a time when Protestant England persecutes Catholics relentlessly. The authorities directed by King James's spymaster in Chief Robert Cecil (Gatiss), hunt down, torture and execute priests while lay Catholics are subject to oppression and the loss of their property. They must practice their religion in secret, risking imprisonment, fines, harassment and even death.

Catesby's refusal to abandon his religion has brought him to the edge of financial, social and psychological ruin. His wife and father have both recently died, leaving him to bring up a young son in an increasingly hostile world.

Unable to stand by while his coreligionists suffer, and despite the peaceful protestations of head Jesuit Father Garnet (Mullan), doing nothing is not an option for a man like Catesby. He starts to recruit friends and relatives, swearing them to secrecy as he devises an audacious plan. His astute and capable cousin Anne Vaux (Tyler) becomes suspicious about his activities and fears the consequences will be the exact opposite of what Catesby intends.

This fast-paced 17th century thriller delves into the history behind the plot evolution, the selection of the team to carry it out, the gathering of the resources, and the obstacles they came up against. At the same time a deadly cat and mouse game is played out with Cecil's ruthless spy network.