Morals by Agreement is unusually pleasant going by the standards of this genre, but the reader should be warned. The going will be much easier if you familiarize yourself with the basic terms and ideas of economics and game theory before you start. On the other hand, Gauthier does explain these terms before he uses them, but he does so very tersely, as befits background material, so these prefatory remarks are among the most difficult parts of the book. Gauthier starts by drawing a connection between the suboptimal outcome of the famous Prisoner's Dilemma of game theory, and the suboptimal outcome of a market afflicted by externalities. Game-theorists look for equilibrium solutions.
Economists tend to look for optimal ones.
Now in many, many interesting interactions, there seems to be no difference between equilibrium and optimality. In fact, the basis of the satisfactory results derived from free markets is that market interaction exemplifies optimal equilibrium. The two classic examples of this are, in game theory, the Prisoner's Dilemma, and in economics, the problem of externalities. Essentially, straightforward maximizers of utility will always choose the action which yields them the greatest expected utility, given their expectations about the actions of the people they are interacting with, under the assumption that those people in turn are also straightforward maximizers. The Prisoner's Dilemma and the problem of market externalities are situations in which interaction of straightforward maximizers leads to suboptimal outcomes.