I’m going to cop out here and quote the book jacket because it’s perhaps the best one I’ve read:
Joshua Then and Now is about Joshua Shapiro today, and the Joshua who was, about being middle aged and being young, about being the parent and being the child. About Then and Now–and therefore set both in the Montreal
of today’s  ultra Separatists and in the smug class-and-race-ridden Canada of yesterday. As well as in London, in Paris, in Ibiza, in Hollywood.” [Not credited] Richler’s wit and cynicism is as sharp and incisive as anyone’s, and it’s in full flower here.
Joshua Shapiro is the son of a pugilist of brief renown-cum-small time racketeer. His mother is from a socialite family who disgraced her family with her low-class marriage. Neither of his parents have a great deal of time or affection for him. His father is often away on “business,” and his mother entertains a series of “uncles” trying to keep house and home together, and she often sends him “out” for extended periods.
Joshua develops a feeling for language, though, and a feeling for inveigling, and he wangles his way into a low paying journalism job despite his lack of education. He turns crusader to report on the Spanish Civil war, but never quite gets there. Eventually, he becomes something of a celebrity columnist and TV commentator. Richler conveys none of this chronologically, and his weaving narrative takes us deeper into Joshua’s psychology and society than any straight line narrative would have.
Despite his prestigious position, there is always a streak of lawlessness about Shapiro, inherited from his parents. In the end, that gets used for good rather than ill, and there may be a lesson in that, but I think Mordecai would be offended if we tried to find one. Certainly if we tried to package this book into a tool for moral instruction. It would offend me, too, so I won’t try.