The Paris Apartment

There was a murder here last night. Who holds the key to the mystery of apartment three?
In a beautiful old apartment block, deep in the backstreets of Paris, secrets are stirring behind every resident's door:
The lonely wife
The party animal
The curtain-twitcher
The secret lover
The watchful caretaker
The unwanted guest
One resident is missing. Only the killer holds the key to the mystery…