Danger, betrayal and cold-blooded murder are all in evidence in the first nail-biting moments of historical drama Gunpowder.
Not for the faint-hearted, the grisly three-part BBC miniseries follows an anti-Catholic parliament in early 17th century England.
Priests and Catholics are being hunted and persecuted under orders of King James I (Derek Riddell).
The laws of then-Protestant England forbid anyone from being a practising Catholic. Anyone who is caught faces the horrific – and fatal – consequences.
But one man is ready to fight back. Game Of Thrones star Kit Harington plays Robert Catesby. He's a devout Catholic who joins forces with Guy Fawkes (Tom Cullen) to blow up the House Of Lords and kill the king.
Today, the infamous real-life event is known as The Gunpowder Plot.
Hot on their heels, however, is King James' right-hand man, Lord Robert Cecil (Mark Gatiss). He's in charge of bringing down the conspirators – at any cost.
"It's a story people think they know," Mark, 51, tells TV WEEK. "But to examine the complexities was very powerful."
While he and Kit co-star in Game Of Thrones, their characters in the HBO hit – banker Tycho Nestoris and Jon Snow – rarely cross paths on screen.
Funnily enough, that's a situation that continues in Gunpowder.
"I'm trying to find Robert the whole time, as we don't have many scenes [together]," Mark says.
"We have one little moment at the end of the season, but that's it!"
The pair did manage to catch up between filming. Sadly, one topic was never discussed: the ending of GOT.
"Kit [who also created and was an executive producer on Gunpowder] keeps all the secrets, so I don't have a clue [how GOT ends]!" Mark confesses.
"But his passion for the project was infectious. He'd come straight from the GOT set and was incredibly tired, but stayed committed."
Although, Mark admits he has given the show's finale some thought.
"I've suggested I should be the last character standing, because if anyone survives, it's usually the bank," he laughs.