Yeah, I was thinking of a different book. Here's the link to the other one:

https://www.amazon.com/Object-Oriented-Programming-COMMON-LI...

For anyone not able to quickly locate the above mentioned items:-

PCL: (Practical Common Lisp): http://www.gigamonkeys.com/book/ (chapters 16 & 17)

Keene: (Object-Oriented Programming in COMMON LISP: A Programmer's Guide to CLOS): http://www.amazon.com/Object-Oriented-Programming-COMMON-LIS...

Warp Speed intro: http://xach.com/lisp/jrm-clos-guide.html