Duality is key, always. As in: love and hate. Fear and risk. Sitting on a park bench lost in thought, and doing lines of coke with an American midget and a couple of prostitutes. Truth, reader, is in the contrast.

As far as Colin Farrell is concerned, the recent film “In Bruges” finds depth without indulgence.

“In Bruges” (Focus Features, 2008) follows hitmen Ray (Colin Farrell) and Ken (Brendan Gleeson) for the duration of their stay in Bruges, Belgium, a picturesque city of medieval architecture, winding alleys, churches and canals. Ray and Ken hide out in the city by order of their eccentric boss Harry (Ralph Fiennes), after Ray ruins a hit – leaving him in a state of self-reflexive aloneness and guilt. And while in Bruges, he inevitably sparks up an inconvenient romance with Chlo?, played by newcomer Clémence Poésy, whose latest work includes a small role as Fleur Delacour in “Harry Potter and the Goblet of Fire.”

A word to the skeptical viewer: Do not see this movie under the presumption that it is a well-spent investment in keeping up-to-date with ironic references to Farrell’s roguish superficiality. As in, the act of Farrell searching for subtle depth as an actor is (surprisingly) not the do-all, end-all humor of this film. Much to my own surprise, Farrell was not cast in this role based upon his artistic merits in shower scenes from “Miami Vice.” Rather, Farrell’s casting reads as grossly appropriate for the self-aware, at times inflammatory, humor of this dark comedy. Bold claim: see this movie, but do not expect, um, what you expect.

The film marks the first full-length effort by Irish director and London native Martin McDonagh, who won an Oscar in 2006 for his live action short, “Six Shooter.” With a background as a playwright, McDonagh had actors training for three weeks before they even set foot before the camera to flesh out the script’s nuances – a process Farrell cited as promoting his newfound appreciation for rehearsal.

“The more we dug into it . it just flew. We knew it inside and out,” Farrell said in a conference call earlier this week.

The film drew largely from personal travel experience – specifically a trip taken four years ago, when as a tourist in Bruges, he found himself torn between visiting the “strange and otherworldly” architecture, and wanting to “get drunk and meet women,” McDonagh said. (See? Duality.)

“Both sides of my brain argued with each other, which became Ray and Ken in the film,” McDonagh said, speaking of constructing the script around the relationship (and perhaps distance) between the two hitmen in the film.

Quick to make an important distinction about his work, McDonagh didn’t want the impact of “In Bruges” to be only in clever script-writing.

“I didn’t want to make a playwright’s film,” said McDonagh, something he characterized as a full-length feature of two men sitting and talking – referencing the hyper-stylized cinematography coupling what Farrell considered a rather brilliant script.

Farrell noted, “It was really deep without being indulgent.”

As far as life experience acquired post-production, Farrell is quick to note his gains: “Herpes, and a few grey hairs,” he joked.

Farrell cited listening to, appropriately, Irish band The Pogues during the process of preparing for the role. And how did he unwind? “A shag’s never a bad thing, truth be told.” Uh, duality?

“In Bruges” will be released in D.C. Friday.