The plot of Elektra in a minute:

Elektra’s father, King Agamemnon, was murdered by his wife Klytämnestra and her lover Aegisth. Now Elektra is out for blood. Conspiring with her sister Chyrsothemis and brother Orest, she seeks to kill Klytämnestra.

As the night unfolds, Elektra becomes increasingly impatient and unstable. When her brother brutally murders both Klytämnestra and Aegisth, Elektra loses herself completely and she succumbs to fatal ecstasy. 

Characters and detailed synopsis:

ElektraDaughter of Agamemnon & Klytämnestra
ChrysothemisElektra's sister
KlytämnestraElektra's mother
AegisthKlytämnestra's lover
OrestElektra's brother who has been exiled

The servants outside the royal palace are debating whether Elektra will come out of hiding today, or if she will continue to grieve her father’s death. They mock Elektra for her madness, as she appears and steers clear of the group. One servant shows support for Elektra, but she is quickly struck down by the others.

Now left alone, Elektra agonizes over her father’s murder, recounting how he was killed by Klytämnestra and Aegisth upon returning from Troy after spending years abroad at war. Elektra declares that she will have her revenge on Klytämnestra. She will conspire with her sister Chrysothemis and brother Orest (whose arrival they await) and butcher both Klytämnestra and Aegisth.

Chrysothemis rushes in suddenly, informing Elektra that Klytämnestra and her lover Aegisth have decided that Elektra will be locked up in a tower. Elektra realizes that she must act quickly, and tries to convince Chrysothemis to assist her in carrying out the plan tonight. Chrysothemis hesitates and wonders if she could actually go through with committing murder. 

Klytämnestra enters, engaging Elektra in conversation, telling her about the nightmares she has been having. Elektra comes off as more cheery than usual, which gives Klytämnestra some hope of reconciliation with her daughter. Elektra suggests that a sacrifice must be made in order to cure Klytämnestra of those nightmares. She then declares that the sacrifice, in fact, is Klytämnestra’s own life. Elektra describes the brutal ways in which Klytämnestra will be murdered, that too at the hands of her own son Orest. Klytämnestra is horrified. 

Two strangers then arrive, and Klytämnestra is taken away to meet them, leaving Elektra alone again.

Chrysothemis runs back to Elektra, informing her that the strangers had brought news of their brother Orest's death. In shock at first, Elektra soon decides that she and Chrysothemis have to complete their revenge immediately. Chrysothemis, however, backs out completely, leaving an enraged Elektra to act on her own.

One of the strangers who came to the palace enters and begins to converse with Elektra. The stranger is eventually revealed to be Orest himself, who had faked the news of his death and adopted a disguise to sneak into the palace. Elektra is absolutely ecstatic that her brother has returned, and the siblings comfort each other.

The hour of vengeance now upon them, Orest heads into Klytämnestra’s chambers and proceeds to fulfill his bloody revenge. Elektra revels in her mother’s panicked screams. Aegisth, Klytämnestra’s lover, arrives in the palace at this moment and faces the same gruesome fate at Orest’s hands.

Possessed by euphoria and madness at this successful double murder, Elektra dances, and dances, and dances, until she drops. Elektra’s fragile mind succumbs to its frenzy.

Orest leaves the palace in silence.