French politics always have been a mess. The backdrop of "La Fronde" as the French civil war was known, is difficult to explain. There were no good or bad guys. The country was thrown into confusion and disarray.
The challenge of adapting the second Dumas novel (as well as the third) is that there is no clear cut plot element to hang your hat on. Unlike the race to get the jewels back from the first novel, "Twenty Years Later" is rather episodic and dis-jointed. the musketeers are no longer musketeers and (in the novel) they are not even on the same side of the political fence.
The movie tries. There is an attempt at the levity of the previous two films. The screenwriters attempt to throw in a weird romance between Athos' son Raoul and Lady De Winter's daughter (an evil son in the book). The writers also keep many of the major set pieces from the book (the fire ship plot against the heroes, the execution of Charles I, the escape of the prince of Condé, etc.) but in the end the film has no spirit.
Everyone involved must have dearly wanted to recapture the magic of the first two films. Lester was working under pressure on a television schedule and budget.
In his autobiography Michael York describes how he looked forward to the first day of shooting. The whole thing turned sour when Roy Kinnear had a tragic (and York believes, an unnecessary) accident. Kinnear was asked to ride his horse across a bridge in a long shot and tried to oblige. He fell and was rushed to the hospital where he later passed away. York feels the producers treated Kinnear and his family shabbily.
Any joy the actors may have had going in to the project evaporated after that.
