Pub plotting
It was Robert Catesby's plan that brought five conspirators to the Duck and Drake Inn in May 1604. Catesby was the brains behind the plot against the king. And he gathered a group of like-minded men, including Guy Fawkes, to help him.
They knew King James I would be attending an important ceremony in the Houses of Parliament on 5 November 1605. That's when they would strike.
King James I at the State Opening of Parliament in 1604.
The gang planned to tunnel beneath the House of Lords chamber, where the king was to attend the State Opening of Parliament. There, the men would plant enough gunpowder to blow up the chamber, and the king along with it.
Why did the plotters want to kill James I?
All the plotters belonged to the Catholic church, and believed they should have more freedom to practise their religion. They also shared an impatience with the rule of King James.
When James became the King of England (and Scotland) in 1603, many Catholics were hopeful he would treat them more favourably than the previous monarch, Queen Elizabeth I. Elizabeth had decided that England's official religion would be Anglican (also called the Church of England), and under her rule Catholics were treated very badly.
Disagreement between religions wasn't new. Fighting and argument in England went back many years.
When James I became king, the situation for Catholics got worse, as many were persecuted for their beliefs.
How to kill a king
All the conspirators had previously been involved in other schemes which tried to win religious freedom for Catholics. In the Gunpowder Plot, the members of Catesby's band each played their part.
Thomas Percy secured a house next to the House of Lords. It became the gang's headquarters where they are believed to have dug a tunnel to the foundation walls of the House of Lords.
Thomas Winter is said to have led the digging of the secret tunnel intended for transporting the deadly gunpowder. Then, in March 1605, Percy was able to rent a cellar directly below the House of Lords - the perfect place to plant their gunpowder.
It was explosives expert Guy Fawkes's job to light the fuse. The plan was then for him to escape to Europe by boat.
The plot unravels
The conspirators successfully smuggled barrels of gunpowder into the cellar, concealing them with wood and coal.
On the evening before the State Opening ceremony, however, their plan hit a snag. Guy Fawkes was discovered in the cellar. One of the men who found Fawkes was Lord Monteagle, a man close to the king.
Fawkes tried to hide his identity, giving a fake name: John Johnson. But his presence in the cellars was cause for suspicion.
A little over a week earlier, Lord Monteagle - a Catholic - had received an anonymous letter urging him not to attend the State Opening on 5 November. There was going to be trouble, the letter warned.
Monteagle shared the letter with the king on 1 November. At first, the king and his government decided not to take action, but to wait to see if more details of the plot came to light.
The arrest of Guy Fawkes.
Following Fawkes's discovery in the cellars, Sir Thomas Knyvett, the Justice for Westminster, ordered a further search. He discovered 36 barrels of gunpowder. Guy Fawkes was arrested and sent to the Tower of London.
Fawkes's capture and its aftermath
Word spread quickly of Fawkes's arrest. The rest of the plotters fled to the Midlands where, in expectation of their plan's success, they had been making preparations for rebellion.
Under torture, Fawkes gave away the names of his fellow conspirators. The authorities pursued them, and several of the gang were killed in a shoot-out.
The rest were arrested and thrown in the Tower of London where they were tortured.
In January 1606, the failed plotters were convicted of high treason and executed. In a bloody display they were hanged, drawn and quartered - the medieval punishment for treason. The heads and other portions of the plotters' bodies were set up at various points around London.
Who sent the letter to Lord Monteagle?
The origin of the letter warning Lord Monteagle to stay away from the State Opening ceremony is uncertain.
The conspirators suspected one of their fellow plotters Francis Tresham, who was reportedly one of the least enthusiastic about the plan. Tresham's sister was the wife of Lord Monteagle, and so Tresham might have been looking out for her benefit.
Another theory is that the letter wasn't genuine, and that it may have come from government circles.
Whatever its origin, the letter seems to have been crucial in foiling the Gunpowder Plot.
The legacy of the plot
To this day, people across the UK celebrate Guy Fawkes Day with fireworks and bonfires as a reminder of the failed attempt to kill King James.
And the monarch's Yeoman of the Guard still search the cellars of the Houses of Parliament before each State Opening ... just in case.
The monarch's Yeoman Guard preparing to search the cellars.