You and Gregory are close friends, and do everything together.
You have a long-standing crush on Charlotte, which she has never looked like reciprocating. More than anything, you want Charlotte to love you - even though she is currently in a relationship with Richard.
You live with Richard and Vanessa, who used to go out. Gregory wanted to be their flatmate, but they turned him down and asked you. You thought Gregory would be upset at you (he's a very intense person) but he has surprised you by not mentioning it. True to form, though, you know he wants revenge on Vanessa and Richard.
You and Gregory have devised a plan to get what each of you wants. By performing a magic ritual during the play, you will cause everything that happens to the characters happen, in a much reduced form, to the actors also. This means that if you make sure you and Charlotte play the right parts, she'll start to really like you. In order for this to happen, either: you must play the Heir and Charlotte play either the Noble or the Guest; or: you must play the Noble, and Charlotte must play the Heir.
At some point in the play, when you and Gregory are on stage together, you must perform the ritual that will make what happens to the characters happen (in lesser form) to the actors from that point on. You must each tell the other, in character, that you are creating this effect, and that you are free from the results of the spell - so that nothing bad happens to you. This must be done as subtly as possible, because if the other actors learn that this is the case, the spell will no longer affect them as much.