Hopefully it's not just gauche nowdays to recommend it here, and that I've not been led astray, but I think ANSI Common Lisp and On Lisp are a great introductio

Hopefully it's not just gauche nowdays to recommend it here, and that I've not been led astray, but I think ANSI Common Lisp and On Lisp are a great introduction sequence and I recommend them both to anyone who wants a methodical but gentle introduction. Among many highlights, the first one has a chapter on raytracing that I found truly impressive in its brevity and significance.