We just had a call from the vets. Riley had FIP. Through work it's a condition I'm familiar with but Riley did not show the classic symptoms. Indeed our vet had never seen it presented this way before. So I know now he never had a chance! It does help to know as I've been going through it over and over, worrying that we did something wrong after bringing him home. Knowing in my heart I hadn't, but my head mulling it over and over .... RIP little man.