"Method" is the careful, systematic way that something intelligent is done. "Madness" is the strange, meaningless action of a crazy person. There is "method to one's madness" when what looks like strange and meaningless action (madness) is actually the result of a carefully reasoned plan (method). Example: "Give me a moment to explain; there is method to my madness." [This idiom comes from Hamlet by William Shakespeare, Polonius speaking: "Though this be madness, yet there is method in it."] Example: "We thought he was crazy to do it that way, but it turned out that there was method to his madness." (Note: Americans usually say "method to one's madness" while British say "method in one's madness." Both are fine to use.)