How did the play end?

I was curious too... found this in a 'study guide':

He heads upstairs to collect his things, at which point Sidney jiggles the handcuffs—the real trick Houdini manacles—and frees himself. He runs to the wall of weapons, grabs a crossbow, and as Clifford stands at the top of the staircase, shoots an arrow into his chest. Clifford falls down the stairs, apparently dead once again. Sidney proceeds to arrange the room to reproduce his original scenario of attempted murder, struggle, and a killing in self-defense. He telephones the police to report the grisly events: “I just killed my secretary. He was coming at me with an ax. That’s right. And wait till you hear this part. You’re going to think I’m drunk but I’m stone-cold sober. I shot him with a medieval cross-bow.”

But as he continues his fantastic story, a hand reaches out from the dark and clutches his throat. Once again Clifford has returned from seeming death to enact his revenge—but this time it’s for real. The young man has pulled the arrow from the cross-bow out of his chest, and now he stabs Sidney with it repeatedly until both the young man and the famous playwright fall dead of their wounds.

A third and final scene concludes the action. Helga and Porter, Sidney’s lawyer, stand in the playwright’s study digesting the astonishing turn of events. Helga, in a trance, explains to the astonished attorney the various feints, ruses, and betrayals Sidney and Clifford have played on them and each other. As they talk, it strikes both simultaneously that the story would make a successful play. In her excitement at the prospect, Helga asserts her right to half the future profits on the basis of her visionary insight into the facts of the case. Indignant, Porter objects, saying that he will be the one to do the actual writing. As they quarrel, Helga threatens to expose to the world her psychic discovery of Porter’s secret use of the telephone: “You speak through handkerchief, in high voice. Say dirty words to all your friends. . . . For shame. . .” Enraged, Porter advances on her “menacingly.” Helga grabs one of Sidney’s knives—they very one she said earlier would be used in a murder—and brandishes it at the lawyer. As the curtain falls, they are circling the desk, she threatening Porter with the knife, while he reviles her with a string of obscenities, two potential killers stalking each other over the authorship of a play.