MINISERIES RETURN: This is the conclusion of a truly, and literally, Herculean labor. It’s the conclusion of actor David Suchet’s commitment to starring in all 70 Agatha Christie stories centered around the self-satisfied Belgian detective Hercule Poirot. It’s a role he began playing a quarter of a century ago, and this final season, number 13, presents the final five stories in the canon, presented as feature-length telemovies. Tonight and next Sunday, PBS presents the first two of those five: The Big Four and Dead Man’s Folly. But here’s the interesting catch – those last three adventures, the culmination of the entire Poirot experience, will be available exclusively on Acorn TV and its Roku channel. More on that later. Check local listings.