4d-Short opera in festive performance thus mounted in islands -9 letters
13a- In Roman squares, coins have to be different 3,1,6
20a- One paid policeman to drop in-he's hoping to strike it rich 10
19d- Fish usEd to be caught -got fearfully small 7
Thanks MarkRae-Yes, I put my question in the wrong section- An even bigger thank you to all you clever people who have found this and helped me when it was hiding in Science !