Detective Conan - Season 1 Episode 735 : The Coded Invitation

A client named Kaori Kitasaka asks Kogoro for help to decode the location in an invitation. Before she leaves, she gives Kogoro her home and cellphone number. After realizing he has deduced and given her the wrong location, Kogoro tries calling her home number but realizes she gave him a fake number. Kogoro calls her cellphone number and she picks up. Kogoro gives her the correct location, Bell Tree Tower, to Kaori. Conan finds her suspicious and figures out Kaori's real home phone number then calls it. He's surprised when Sato begins talking to him on the phone and the group discovers that a gun (Nambu Taisho 14) is missing from Kaori's home.