Algy figuring out that Jack has been leading a double life as Jack and as Earnest.
It's mine it doesn't matter that the cigarette case says "Jack"
Jack getting interviewed, and finding out the truth of his family.
I don't have parents. I was left in a handbag.
You are a disgrace, and do not have permission to marry Gwendolen.
Algernon, under the name Earnest, comes to Jack's country house to meet Cecily, and proposes to her.
Gwendolyn meets Cecily, and they both believe the same Earnest has proposed to them.
The boys admitting that neither of them are Earnest, which causes the girls to get mad at them.
Neither of us are Earnest!
Jack finds out that Miss Prism left him in the handbag, and that he is actually Algernon's brother and cousins with Gwendolyn. This means Cecily can marry Algernon, and Jack is still marrying Gwendolyn.