I don't believe very much in the "slow" introduction.
This is how I do it: 1)we let the newbie in the livingroom, together with us and all the other cats. Attention: supervising from humans is absolutely necessary. 2)Whenever we pan to leave for a while (shopping, etc. ), we seprate them again, and put the newbie in the bathroom where she loves to be. 3)Feeding time: I fil all bowls, then I call the cats, and show the newbie her bowl. 4)I let them be together all day long . There is some hissing, but that is only normal! 5) Once that the "oldies" accept the little one completely, I let them all sleep together in their cat-room

I know that most people use the "slow" introduction. But I have done this with all my cats, and it DID wok very well, right