A bit of a dilemma or what would you do question. Here's the text of the part of the mystery I have a question about:
When this card enters play, place a Mystery token on Plateau of Leng. As an encounter, an investigator on Plateau of Leng may attempt to bind the dark god to another world. He draws and resolves an Other World encounter. If the effect allows him to "close this Gate", he may spend 1 Clue to place 1 Eldritch token on this card.
The dilemma arose to the somewhat unlikely coincidence that there already was an open gate on Plateau of Leng. Could an investigator attempt to close that gate, spend a clue, and both close that gate and place an Eldritch token on the mystery, thus killing two birds with one stone?
My gut tells me no, with that "as an encounter" wording, but we were in such bad shape that the group OKed it.