I've only read Conceptual Mathematics; sorry for the confusion.

CM covers Category Theory as a general tool for probing and exploring algebraic concepts beginning as simply as endomorphism and extending all the way out to how it can be the foundations of a generalization of set theory via Toposes... all in a cheery and explorative fashion which really illuminates why the ideas work instead of merely stating them.

I'm not sure what the required background might be, but it's probably pretty minimal.