If you have confidence in your hunch, you could pop in for that cuppa on your next rounds - with a friend, though (I wouldn't go alone if I were you, you need a witness).
Decline the alcohol too (you're on the wrong meds etc.) and talk with raised voices. If Evie is in there she'll go crazy at the sound of your voice and you'll hear her.
Take care when accusing people of untoward activity. She may well be completely innocent. If not she's likely to be unstable, or just terribly lonely, but either way if she's caught out kidnapping other peoples' pets she's unlikey to be delighted about it.
Is Evie microchipped? If so, she's legally yours and anyone knowingly attempting to take her is technically committing theft.