The R&B star Chris Brown is facing claims in a lawsuit that a woman was repeatedly raped by a friend of his during a drug- and alcohol-fueled party at his Los Angeles house last year.

Gloria Allred, a high-profile women’s rights lawyer, filed the suit against Mr. Brown on Wednesday on behalf of a woman who says that she was held against her will at his house in February 2017 and raped by his friend Lowell Grissom Jr. He is also named as a defendant in the suit.

The woman, called Jane Doe in the suit to protect her privacy, is also suing a woman who the plaintiff says forced her into a sexual act. The female defendant is called Doe X because the accuser did not know her name. Fifty other people are listed as defendants, all unnamed because the accuser did not know their names.

“This is one of the most horrific cases involving alleged sexual assaults that I have ever seen,” Ms. Allred said at a news conference on Wednesday. She said her client had been “severely traumatized.”