does the plot make sense?

For a moment, forget what happens in the film and just suppose you had been given a suitcase that is not your own but bears a label with someone else's name on it.
You have found out where that other person is staying.
Wouldn't your first reaction be to ask her if she has your suitcase? And if she has, could we please swap because you have hers?

Furthermore, the fact that the other suitcase has a label with the owner's name would indicate that she was not involved in a plot to steal your suitcase. So what would be the point of kidnapping her?

Also, imagine you are the kidnapped wife. Presumably, fairly early on in your abduction, your captors might bring up the subject of a missing suitcase. Then, even though the idea has been beyond their powers of deduction, you would realise that the mysterious case you had in your hotel room was what they were looking for. At that point you would say to them: "I've got your case. You can have it, just let me go and we'll forget all about this little episode."
Maybe she did say that; and maybe they said: "No, that would be too simple! We'd prefer to have the police on the case and for there to be a few killings."

i never understood why they kidnapped her.. they lured her downstairs.. why not just say "excuse me but you have our suitcase can we have it back please" but then there wouldnt of been a film lol.