Poor you
Cat pee is revolting. We had a similar problem recently, our elderly cat developed incontinence due to the stress of having our new baby in the house. I googled 'cat urine removal' and found a combination of baking soda and vinegar which worked really well. Also you can add hydrogen peroxide to the mix - just as long as its on things that won't lighten (not carpet!).
Did it come through a cat door? If you still need to use your cat door for your own cat, those magnetic ones are great - and they keep all the riff raff out 
Good luck