Let’s start with the ending to “Roman J. Israel, Esq.,” and no, I’m not going to even hint at giving anything away, but I have to say:

It’s one of the most underwhelming and perplexing endings of any movie I’ve seen in quite a long while.

The ending ends, but then it kinda keeps going with no real sense of purpose — and that doesn’t help matters at all, because all it does is give one time to reflect on the story and the characters we’ve just met, and lament that strong performances from Denzel Washington, Colin Farrell and Carmen Ejogo were ultimately lost in the fog of a strange and confusing and bumpy and sometimes implausible story line.

As the final scene in “Roman J. Israel, Esq.” (and how’s that for a title that trips the tongue) lingers on, no doubt some viewers will be waiting for one of those end-credits codas where we learn about the real Roman J. Israel and the impact he had on the world even after he was gone.

But writer-director Dan Gilroy’s ambitious but muddled legal thriller isn’t based on or inspired by a true story. It’s pure fiction. This is a 21st century legal crusader tale that harkens back to films such as “… And Justice for All” and “The Verdict” and “Presumed Innocent” and “A Time to Kill” and “The Rainmaker,” but it lacks the dramatic impact and the tick-tock intensity of those films.

Sporting an unruly Afro, decidedly unstylish eyeglasses and ill-fitting clothes, and looking like he’s long overdue for a trip to the dentist, Denzel Washington’s Roman J. Israel is an obsessive-compulsive, socially inept, astonishingly brilliant legal savant who has spent some 25 years working behind the scenes on behalf of L.A.’s downtrodden. Roman always did the research and constructed the legal arguments, almost never setting foot in a courtroom.

When the small firm Roman works for suddenly closes, he finds himself lost and virtually unemployable. Finally he reluctantly takes a job with a huge law firm run by George Pierce (Colin Farrell), a slick shark who represents everything Roman has long despised about the criminal justice system.

The dynamic between Roman and George seems to be the central focus of the film — until it suddenly isn’t. Washington and Farrell are electric in their scenes together, as a little bit of Roman seems to be rubbing off on George, and vice versa.

In the meantime, Roman has made quite the impression on a passionate civil rights activist named Maya (Carmen Ejogo), who practically worships Roman for his quarter-century of commitment to the oppressed and the forgotten. It appears there might even be a romance brewing — but when Roman and Maya meet for dinner, let’s just say the speech Maya delivers seems WAY over the top. All of a sudden a character who seemed strong and focused and deeply connected to the real world comes across as shockingly blind to certain realities right in front of her.

Even more problematic is a decision Roman makes that contradicts just about everything he’s ever stood for. It sets off a chain of events that put lives in danger but also stretch credulity — particularly when Roman finds himself alone in a room with an accused murderer, and the conversation goes from tense to you-gotta-be-kidding-me.

Later there’s an even more perplexing scene, when a major character sees a violent crime is about to be committed in a very public setting — and behaves in a manner that makes zero sense.

“Roman J. Israel, Esq.” has pockets of intrigue, and writer-director Gilroy and Washington have teamed up to create a promising dramatic character.

We just never get full delivery on that promise.

★★

Columbia Pictures presents a film written and directed by Dan Gilroy. Rated PG-13 (for language and some violence). Running time: 129 minutes. Opens Wednesday at local theaters.