Loud Crime in a Paris Bank

In Paris, on Montmartre, there is a commotion! Three suspicious guys are digging a tunnel under the sewer, spying on the locals, and behaving extremely suspiciously. What are they up to? Kidnapping someone? Robbing an apartment? Or maybe even... robbing a bank?! Meow, mustachioed ones! It's time to sniff out what's going on!