The Last Toast at Hotel Sondera

At 12:47 a.m., the final toast at Hotel Sondera ended with an overturned chair, a lipstick-marked champagne glass, a blank ninth line on the guest list, a room key left on a silver tray, and one guest gone before the music stopped. Complete the scene, examine the evidence, and determine where the secret meeting was meant to occur.

Which room number is connected to the secret meeting, and where was the meeting supposed to happen?