An analysis of the title four loves -- affection (storge), friendship (philia), erotic love (eros), and charity (agape). Plus some poking around in the lower levels, with our likings for things. And analyzing all of them in light of Need love, Gift love, and Appreciative love. . . and the virtues and weaknesses of the first three types.
An interesting book. I have also heard it recommended as invaluable in shipping discussions, which strikes me as quite possibly true.