Stay in the closet and hope he leaves again when he finds you not there.
From Create Your Own Story
You put your hand over Kara's mouth and lean over to put your ear on the door. Hearing Adam enter the room and calling your name, you stay silent as you don't want him to get suspicious of the closet that you and his half-naked sister are in. But as your are listening, you feel Kara's ass rub up against your crotch even more. You move your hand from her mouth and she smiles at you and winks.
Kara whispers, "I can try to stay quiet, because right now I really need your cock in my pussy." Pushing her ass even harder against your cock.
You listen for Adam once more, but it seems that he has left the room. You look down to see that Kara has removed her thong and has now exposed her beautiful ass and virgin pussy to you in their full glory.
