In the new film “Secret Window,” main character Mort Rainey tells moviegoers “The most important thing is the ending.” Ironically, it seems screenwriter-director David Koepp (“Stir of Echoes”) missed that memo.

In “Secret Window,” based on the Stephen King novella “Secret Window, Secret Garden,” Koepp serves up a physiological thriller with a twist; one that refreshes audiences at first, but leaves a funny aftertaste.

The plot immediately seizes your attention to such a degree that thoughts of restroom and popcorn runs become a distant memory. Koepp weaves an intricate and captivating tapestry with nail biting suspense, witty humor, and mind bending mystery that suddenly and somewhat disappointingly unravels in the film’s final moments.

Oscar nominee Johnny Depp stars as Mort Rainey, a successful writer struggling through a painful divorce and a severe case of writer’s block. He holes himself up in a lakeside cabin where he spends his days in his ex-wife’s tattered bathrobe, noshing on Doritos in between countless catnaps and bouts of self pity.

Rainey’s life is painfully uneventful until John Shooter (John Turturro), an unsettling whacko with a Mississippi-backwoods drawl, turns up on Rainey’s doorstep accusing him of plagiarism. “Yew stol’ mah stowry,” the crazed southerner drawls from beneath a black dairy farmer’s hat.

To force the writer to make amends, Shooter will go to any lengths, including stalking and murder. With only a few days to prove that his story is his own, Rainey scrambles to figure out Shooter’s true identity before the Mississippian makes good on his threats to burn Rainey’s life and everything in it.

It is no secret that any and all success “Secret Window” encounters is credited 100 percent to Depp’s unique and unparalleled talent.

Fresh off his Oscar nomination for his role as the eccentric Captain Jack Sparrow in Disney’s wildly popular “Pirates of the Caribbean,” Depp hurls himself into the new role, bringing life and dimension to Rainey’s otherwise wimpy character.

He effortlessly pulls off Rainey’s complex and troubled demeanor and instantly wins the audience over with his dry wit and brilliant signature improvisation.

Depp’s solitary scenes and inner monologues make up the film’s most memorable moments; no supporting actors necessary. In “Pirates,” Depp steals the show. In “Secret Window,” he is the show. Cast any other actor as Mort, and the movie would fall apart faster than Rainey’s life under Shooter’s demands.

John Tuturro (“O Brother, Where Art Thou” and “Mr. Deeds”) also gives a solid performance as Shooter, the crazed southerner out to get Rainey. Tuturro’s Mississippi drawl is delivered naturally and authentically, never appearing forced or contrived.

His slow and distinctive speech is so eerie it sticks in your head for days. As a whole Tuturro’s performance is an inspired balance of both humor and disturbing unpredictability, allowing him to more than hold his own against Depp.

In addition to Depp and Tuturro’s flawless performances, an honorable mention must go to “Secret Windows” silent star, Johnny Depp’s hair. The bleached unwashed devil-may-care coif changes style and character every frame and often provides much needed comic relief. The silent scene stealer might just rival its owner at next year’s Oscar with a nomination for best supporting actor in a comedic role.

“Secret Window” has suspense, intrigue, wit, and incredible talent, but it is still missing one major element, the most important element in Mort Rainey’s eyes. That missing link is a credible ending.

The film maintains a captivating beginning and middle but then takes a tragic turn towards the bizarre. Although some audiences will be shocked by the film’s twist ending, others might find it a tad predictable, or even down right absurd.

The bottom line: despite the film’s abnormal finish, the majority of “Secret Window” is so riveting and engaging it’s still worth the $8.50 to see it in theaters.

Make no mistake though, it is entirely to Depp’s credit that “Secret Window” actually ends up an entertaining thriller movie.