I need a short plot overview of Emma by Jane Austen, please.

The story is told from the point of view of Emma Woodhouse, a rich, snobbish (but in the end lovable) young woman whose life is upended as the novel begins with the marriage of her governess Miss Taylor to their neighbor, Mr. Weston.
Emma fills the hole left by Mrs. Weston's marriage with a new companion, the young and pretty Harriet Smith. Emma plots a marriage between Harriet and the local clergyman, Mr. Elton.
The notable fact about Emma is her cluelessness. The novel is famous because it is channeled through the perceptions of a heroine who misses what is right in front of her eyes. First, she fails to see what we as readers do: Mr. Elton wants to marry the rich and established Emma, not the penniless Harriet of unknown parentage. Emma's mix up over this leads to the dark comedy of the first part of the novel.
Later in the novel, Jane Fairfax and Frank Churchill arrive on the scene. Jane is beautiful and accomplished but penniless. Frank, the son of Mr. Weston, is wealthy, having been adopted and raised by his rich Churchill relations. He is dependent on Mrs. Churchill for his money and does not dare offend her.
Frank is secretly engaged to Jane. He can't marry her without Mrs. Churchill's approval. That approval is not likely to be coming, hence the secrecy. We don't know of this engagement until the end of the novel.
In the meantime, Franks flirts with Emma, using her as a decoy so that nobody will suspect he is in love with Jane. Because Emma is clueless, she falls for the idea of Frank being in love with her. We as readers usually do too because we see the world through Emma's eyes.
After the shock of the Jane and Frank engagement quickly wears off, Emma turns to Mr. Knightley, her brother-in-law. Though they have had a quarrelsome relationship throughout the novel, they realize they are in love, and so the novel ends happily: Jane ends up with Frank, Emma with Mr. Knightley, and Harriet with her first love interest, Mr. Martin.