On New Year’s Eve 1999 at Blackadder Hall, Rowan Atkinson as Lord Blackadder hosts four guests and boasts that he’s built a time machine from Leonardo da Vinci’s plans. The attendees—Archbishop Melchett, Archdeacon Kevin Darling, Major George, and Lady Elizabeth—are played by a stellar lineup: Stephen Fry, Tim McInnerny, Hugh Laurie, and Miranda Richardson. He bets £10,000 that he can fetch back any item from history they desire, prompting them to name a Roman centurion’s helmet, the Wellington boots worn on the day of the Battle of Waterloo, and an ancient pair of 200-year-old underpants. The whole thing turns out to be a ruse: Baldrick, played by Tony Robinson, has actually retrieved the items from storage, and the “time machine” is merely a prop. Still, Blackadder stages a pretend voyage, with Baldrick hiding inside, until the door unexpectedly works and they really do travel through time.
Their first stop is the Cretaceous period, where a towering Tyrannosaurus Rex confronts them. They discard their wager items and eventually manage to defeat the beast using the underpants, a twist that comes to light when Baldrick confesses that he never wrote dates on the dials. With no dates, they realize they cannot return to the present, and the pair must navigate history by improvisation alone.
They return to 1999’s audience only to find a twist: they land in the era of Queen Elizabeth I, with Blackadder again at risk of a beheading unless he can present a suitable gift. He digs into his pockets and pulls out Polo mints, which the Queen adores, rewarding him with her crown and charging him to bring back more “minty things.” During this chaotic excursion, Blackadder meets Colin Firth as William Shakespeare and secures an autograph that he wittily uses later, exclaiming, > "that is for every schoolboy and schoolgirl for the next four hundred years." The encounter sets the stage for a far-reaching imbalance in history and culture.
Next, the time machine drops them in Sherwood Forest, where they are captured by the Merry Men and face the grim reality of their outlaw lifestyle. Blackadder questions Robin Hood’s ethics—why steal from the rich and share with the poor, who would choose a life with no toilets or comforts—and the Merry Men, outraged by the philosophical challenge, shoot Robin Hood. In a bold turn, Blackadder engages in a dalliance with Maid Marian, before leaving with Robin’s hat as a memento of this strange encounter.
The journey continues to the Battle of Waterloo, where Blackadder arrives to steal the Duke of Wellington’s boots, hoping to win the wager once and for all. The odyssey then moves to Hadrian’s Wall in Roman Britain, where they glimpse their Roman ancestors and snatch a helmet, narrowly escaping a charge from Picts.
Baldrick offers a macabre memento about life flashing before dying, and Blackadder seizes the chance to learn how the dials were set by shoving Baldrick’s head into the time machine’s toilet. The plan works, and Baldrick remembers the crucial settings needed to return home. As they reflect on their travels, Baldrick quips that anyone might change the world for the better, while Blackadder contends that most people can only improve their own fortune.
Back in 1999, the guests marvel at Blackadder’s haul, but history has been altered: Robin Hood is now unknown, Shakespeare is remembered only as the inventor of the ballpoint pen (a detail he left with them after their encounter), and Britain has fallen under French rule since Waterloo. Realizing his meddling has destabilized the timeline, Blackadder races back into the machine to set things right. He renews his praise for Shakespeare, charms Robin Hood, and restores the Duke of Wellington to his rightful place, aiming to fix the broken history he created.
When they finally return, Blackadder and Baldrick secure the winnings and usher everyone upstairs to watch the Millennium Dome celebrations. He hints at a new, audacious plan, whispering to Baldrick that there is a “very, very, very cunning plan” as they vanish once more into time. In the final tableau, Blackadder reappears as an absolute monarch, King Edmund III, married to Queen Marian of Sherwood [Kate Moss], flanked by a figurehead Prime Minister Baldrick, and the royal procession marks a new, if precarious, reign.
