I think cat sprayed but I can't pinpoint where!!!

Yesterday, my husband was petting my younger cat and it "expressed" itself all over him. I cleaned up as much as I could but the cat ran upstairs. Now I have another cat who has litter issues so I can't tell WHO did it, but on the top landing of the stairs, I smell "pee". But nothing is wet at all!!

This morning, my younger cat (the one that expressed) sniffed around a certain location. I got down on all hands and knees, put my face to the carpet and I could smell it. So I scrubbed it as clean as I could. But the smell is still there. So either I'm "off", or I didn't get it all.. 

But I don't get it, nothing was wet to indicate that a cat might have peed. It's all dry but it SMELLS like pee.

Advice?

Should I just go get a bottle of Nature's Miracle and douse the area?

I think a way people see where cat pee is, is to use a black light.

(Haven't had this problem, touch wood, so that's all the help I can give, I'm sorry!!)

Updated: I literally just bought a bottle of Nature's Miracle and doused the general area. I was very generous. It's fine now.