The thief is the "shady guy" (aka strange man) with a scar, not the Black Widow. The term Black Widow always applies to a female, and was originally used for a woman who repeatedly remarried, having killed each of her husbands (as the black widow Spiders kill their male mates).
The boat captain suggests the mimes Downtown, who only answer by pantomiming "music". This suggests the All That Jazz cafe (which is empty if you check first).
The Black Widow is never in the museum (at least not as the Black Widow).
skrow you
The Black Widow (veuve noire) is posing as the police inspector, whose house is in the Country Side. It is on the far right of Counterfeit Island.
you can't
in the inspectors cottage
beat the black widow
the black widow
in the lair of black widow
you go to the art musem
You don't have to find the Black Widow. She will find you. (Check the colorful painting.)
You beat her. She's in prison.
the bad guy for counterfeit is the black widow