If I want to say "Waiter! There's a fly in my soup!" (A line from a classic American comedy skit for those unfamiliar) I guess I would say "Офіціант! Це муха в мій суп!" Just an educated guess.
Thank you! I'm not yet familiar with the grammar form you used. Going by context, is that locative case?
Also I edited for the correct case :) Sometimes even natives get confused
You're welcome! Honestly I'm not sure how they called in English, I'll try and look it up for you when I get home