What do Cecily and Gwendolen discover when they meet and chat over tea?

They are both engaged to Earnest Worthing

They are actually long-lost sisters.

They like all the same foods.

They realize they are both engaged to a man named Ernest, but they soon discover that they are engaged to the same man, who goes by the name Ernest Worthing in the city and Jack Worthing in the country. This causes some confusion and conflict between the two women.