A Search for Evidence

Looking for evidence that her husband may have been unfaithful, a woman is in a hotel, accompanied by a witness, and they are peeking through the keyholes at the guests. After looking at a couple of rooms inhabited by strangers, they see a tray of drinks taken into room #9, but the room turns out to be occupied by a group of men playing cards. Still the wife continues, sure that eventually she'll find what she's looking for.