 Basil has secretly invited their closest friends to Fawlty Towers for the occasion.Before they arrive, he pretends to have forgotten again in order to maintain the surprise.When Sybil asks him if the date reminds him of anything, he guesses random anniversaries, such as the battle of Agincourt, the battle of Trafalgar and Yom Kippur (none of which actually happened on 17 April).