Denzel Washington is one of Hollywood’s finest actors, a guy who can handle both serious drama in films like “Fences” and action in countless thrillers, such as “Man on Fire” and “Safe House.” He brings the two genres together in a way that few others can, adding serious moral weight to films that most other movie stars would allow to just be laden with cheap thrills.

Aside from his villainous Oscar-winning turn in “Training Day,” perhaps the best example of Washington’s genre-blending is his 2014 hit “The Equalizer,” one of the films in his lengthy career to break $100 million at the US box office. That success inspired Washington to make “The Equalizer 2,” the first sequel of his career, and judging by the huge response it received in landing in the top spot on the box office charts last weekend, it won’t be the last.

In the films, Washington plays a former CIA operative named Robert McCall, who made a deathbed promise to his wife that he would leave his shadowy, violent career behind. But just as he was drawn into helping others using both his investigative and fighting skills in the first movie, McCall opens the sequel on a train that’s hurtling through Turkey as he finds and confronts a man who kidnapped his daughter out of spite for his wife.

This first showdown comes fast and furious in the opening minutes, as a James Bond-style prologue that has nothing to do with the rest of the plot. Within five minutes of his return to Boston, McCall is kicking ass on a smug group of young power brokers who drugged and assaulted a female intern, and in filling his endless free time as a Lyft driver we see that McCall subjects himself to sadness from all levels of society.

But then, out of nowhere, viewers see a group of thugs in an apartment in Brussels, Belgium, shooting a wife and mother in the head before shoving the gun in her husband’s mouth to make it look like a murder-suicide. The only reason given for this horrific double murder is that the man’s name was on a list — a list that the movie never bothers to explain.

One has to guess that the husband was a CIA operative of some sort, because McCall’s former agency associate Susan (Melissa Leo) appears in Brussels trying to solve the crime. Just as she’s about to have an idea about who the killers are, she’s attacked by two different thugs, who wind up dead themselves in an explosion soon after.

McCall realizes that there’s something big at play and springs into action to avenge Susan’s death, but the revenge part of the story is barely fleshed out — we never learn why anyone involved was killed in Brussels — and the villains lack compelling motivation or even barely any personality. Weak villains are also a problem in another current thriller, “Skyscraper,” leaving one to wonder how studios can invest $60 million into “Equalizer 2” and $125 million on “Skyscraper” without insisting the stories are compelling on every level.

Thankfully, the action is expertly rendered, though a climactic showdown amid a hurricane feels like it was created for the wow factor of battling in a raging storm than for any valid plot point. It’s doubly frustrating that screenwriter Richard Wenk settles for such poorly drawn villains and a flashy yet hollow climax, since the film’s subplots are beautifully written and humane tales that give Washington and his fellow actors plenty to sink their teeth into.

The main subplot follows McCall as he tries to mentor a bright African-American teen named Miles (Ashton Sanders), who has incredible artistic ability, yet is undergoing extreme peer pressure to join a local gang. This storyline results in a powerful monologue by McCall, making an impassioned case for Miles to show personal responsibility and break through the hopeless mindset that traps far too many young black men in our cities.

It seems clear that Washington and director Antoine Fuqua — who worked together previously on the first “Equalizer,” “Training Day,” and “The Magnificent Seven” reboot — are a terrific team who try to add valuable messages to their genre work. “The Equalizer 2” is an entertaining time at the movies, but if they had only insisted on closing the plot holes and making a vivid villain, it could have been an outright classic. n

“The Equalizer 2”: B