*The Theory of Finite Groups" by Kurzweil and Stellmacher is not as comprehensive as Aschbacher's book and its first half is a good introduction for beginners, but its second half (Quadratic Action, The Embedding of $p$-Local Subgroups, Signalizer Functors and N-Groups) goes quite deep and shows also in some special case how to classify simple groups that are $N$-groups, i.e., groups of even order with all $2$-local subgroups solvable [usually $N$-group is the stronger condition that all $p$-local subgroups are solvable]. –  j.p. Jan 31 '13 at 12:21