On New Year's Eve 1999, the modern-day Blackadder is hosting a dinner party for the latest, 20th-century incarnations of Melchett (a Bishop), Darling (a Reverend), Elizabeth (a titled lady) and George (an Admiral). As Blackadder's regular cook has a night off (attending an orgy at Delia Smith's place) dinner is being prepared by the 'man who fixes the septic tank', none other than Baldrick.

After dinner, Blackadder announces that he has constructed a time machine based on drawings left in a Leonardo da Vinci sketchbook. This is met with hoots of derision and cries of disbelief from the gathered party, so Blackadder wagers them £30,000 that it is true, and as proof offers to fetch any historical artefacts they wish. They decide on the Duke of Wellington's actual Wellington boots, a Roman Centurion's helmet and an authentic pair of 18th-century underpants. The whole scheme is, of course, an elaborate scam involving Baldrick and a cellar full of historical artefacts. Baldrick, however, has built a time machine to da Vinci's blueprint and it works, propelling Blackadder and himself to various past times where they wreak havoc with history.