In his early films (e.g. “Night Shift,” “Beetlejuice,” “Mr. Mom”), Michael Keaton epitomized the word “manic.” His over-the-top comic portrayals during that era were box office gold. But then he made a lane change and proved his dramatic acting chops in movies like “Clean and Sober,” “The Paper,” and even Tim Burton’s “Batman.”

Since then, he’s stayed in that lane, which afforded him the opportunity to do quality supporting work with directors like Quentin Tarantino (“Jackie Brown”) and Steven Soderbergh (“Out Of Sight”). He then spent 15 years off the radar in projects that aren’t worth mentioning before making a big return in “Birdman,” for which he was nominated for an Oscar. He gained more acclaim for “Spotlight,” “The Founder,” and the terrific Hulu limited series, “Dopesick” (for which he won an Emmy).

Now Keaton is firing on all cylinders in “Knox Goes Away,” a movie he directed which got short shrift when it was released in theaters earlier this year. But it’s now finding an audience by streaming on Max.

Keaton plays John Knox, a professional killer with a problem. He’s been diagnosed with a fast-moving form of dementia and only has a few weeks before his brain turns completely to mush. Knox goes out on a job with his partner, Muncie (Ray McKinnon, whose face screams “perfectly cast!”), but things go south. On top of that, Knox’s estranged son Miles (James Marsden) shows up with his own can of worms and asks his father for help.

Meanwhile, police detectives Ikari (Suzy Nakamura) and Rale (John Hoogenakker) find several pieces of evidence that point them in Knox’s direction. He knows that, so he has to figure a way out of these messes before he’s caught and his mind goes on a permanent holiday.

Writer Gregory Poirier has written a clever plot that gives the cast (including Marcia Gay Harden in a small role as Knox’s ex-wife) plenty of opportunity to showcase their talents. As for Keaton’s acting, it’s the best I’ve seen him offer in a long time.

He does so much with his eyes and face, keeping his voice calm yet saying so much. In a few scenes he lets the camera linger while his character is just thinking, and he makes even that compelling. There are others where we can see Knox’s silent frustration as he struggles to remember simple words like “car.” The look on Keaton’s face reminded me of my own father’s during the long battle with dementia that eventually took his life. Heartbreaking.

Keaton’s direction is sure-handed. He opens “Knox Goes Away” with moody jazz music that creates the atmosphere of a classic film noir. He doesn’t do anything fancy with the camera, but every angle is perfect and he plays with splashes of light across characters’ faces. He also keeps everyone from overplaying their roles — including the notorious scenery-chewer Al Pacino, who gives one of his lowest-key performances in a long time.

The moment the movie was over, my wife was texting her friends to tell them to watch it. I felt the same way, which is why I’m recommending “Knox Goes Away” to you with a rating of 9 out of 10.

Now streaming on Max.