21 London Road is the place where the late Jacob Balthazar rented an apartment in the book The Broken Ear. This address is the residence of Jacob Balthazar's landlady, the unseen Mr. and Mrs. Dove, Polly the Parrot, and Colonel Barker.
Tintin makes his way to this location after reading in the paper about Jacob Balthazar's sudden death. Upon arriving he discovers several clues that this was not an accident but a murder. Just as Tintin left London Road he gets the idea of buying the Polly the parrot but just as he gets back Jacob Balthazar's landlady splits the news that another man has already bought the bird. The man does not have the parrot for long however as it escapes when he gets into a 'regular punch up' with a rather large gentleman who thought the parrot's insulting language was coming from the man.
Jacob Balthazar's apartment
This location appears again when Jacob Balthazar's Landlady awakes to the sound of 'ghost of Jacob Balthazar'. This theory is cut short however when Colonel Barker finds out the sound was from Polly who had returned to the flat.