The moviegoing public needs more Hollywood films like "Source Code." It's not that it's perfect or even close to it, but it's complex, thought-provoking, and uses a science-fiction-tinged storyline to speak eloquently on such existential topics as the unpredictability of life, the opportunities we so often let pass us by, and the appreciation we should have, but rarely do, in regards to the world around us. An impressive sophomore effort from director Duncan Jones (2009's "Moon"), the picture is a completely original work written by Ben Ripley—not a remake, or a sequel, or an adaptation of a novel or short story. The frequently mind-bending plot, wrapping in and out and back on itself as it time loops again and again, keeps the viewer engaged, but it's the sympathetic attention to its characters and their urgent connections with each other that give the audience a reason to care.

Colter Stevens (Jake Gyllenhaal), a helicopter pilot who has been stationed in Afghanistan, awakes on a commuter train headed for Chicago. Seated across from him is the sweet-faced Christina Warren (Michelle Monaghan), who acts like she knows him well, but keeps calling him Sean. In exactly eight minutes, both of them—and everyone else onboard—will be dead from a planted bomb that blows the locomotive to smithereens. Colter suddenly comes to in a dark, tightly-quartered shell of a room, corresponding via computer screen with a mysterious organization called Beleaguered Castle. Technician Carol Goodwin (Vera Farmiga) is guarded about what she tells him, but the details slowly come into focus. Colter was mortally injured in the line of duty, and the company is using the activity left in his brain to try and find out the identity of the bomber. With time running out, Colter will be put in another man's shoes in order to relive the same eight minutes over and over until he completes his mission. The more time that he spends in a reality that has already taken place, the more determined he becomes in finding a way to save Christina and the rest of the passengers from certain death. Indeed, if given the chance, is it even possible to alter the past?

"Source Code" is not about time travel, per se, but about, as Carol explains it to Colter, "brain reassignment." Returning to the moments prior to the train explosion is a means to one end—to figure out who is behind the bombing so that the terrorist can be caught and another impending crises averted—and nothing more than that. Yet, what would happen if he did manage, in the span of those eight crucial minutes, find the explosives, the person behind it, and somehow stop this horrible event from happening? Would it send the world into an alternate reality? What might happen to the old present-day? For a motion picture that intimately revolves around the same limited timeframe, it's truly fascinating, even invigorating, to see how Colter's different actions throw the rest of what surrounds him on a different course—but, ultimately, the same general outcome. The existing possibility that things can be set right for the doomed passengers keeps one's interest high. It also makes the viewer wish he or she could get to know these characters better, particularly Colter, Colter in the body of Sean, and Christina. One imagines these people, all of them immensely enjoyable to be around, floating into a different story, or coming alive long enough to be seen in their everyday lives. They're that engaging.

The screenplay is trim and compact, not a second wasted, but it is the striking appeal of Jake Gyllenhaal (2010's "Love and Other Drugs") and Michelle Monaghan (2010's "Due Date") that raises the film above the level of a crafty technical exercise. Though nothing is ever spelled out—and thank you again, Ben Ripley, for not dumbing the writing down with lots of extraneous exposition—the viewer is able to piece together that Colter's temporary alter-ego, Sean, rides the train into the city every morning with Christina. They're more acquaintances than friends, but keep each other company during their commutes and are edging toward flirtatious territory. They're probably soul mates, but neither of them have yet made a definitive move. The nagging urgency between them is partially grown from their approaching fates, but also from the viewer's wish that they would act now, get their feelings out in the open, and do something radical to hopefully revamp the sad destiny that has already occurred. Gyllenhaal brings desperation, intensity, and contemplative pathos to his role of Colter Steven, a man who must deal not only with the reality of the end of his life, but the fantasy of a relationship he can't have because it's not really his. As Christina, Monaghan is incandescent, never before quite as lovely as she is here. By unknowingly going through the same loop, it is the differences between each attempt in Monaghan's role and the way she reacts to Sean's behavior that suggests rather succinctly the many possibilities of roads not taken.

"Source Code" opens with glorious aerial photography of downtown Chicago, presented as a place both familiar and innately one-of-a-kind. Cinematographer Don Burgess's (2010's "The Book of Eli") lensing is immaculate; this particular city hasn't been captured with such vitality since probably 1986's "Ferris Bueller's Day Off." The full-bodied orchestral score by Chris P. Bacon (2010's "Love Ranch") is thunderously confident, but never overbearing; it serves its purpose to the narrative exceptionally. If there is one element that gives pause, it is the picture's ending, a careful balancing act between the grittiness of its fictional science and the sentimentality of its romance. Director Duncan Jones deceptively goes in one direction that suggests a transcendent bittersweetness, a symbolic, slightly ambiguous comment on life's continuation even in death, but then does an about-face and concludes on a different note. The more the viewer assesses its details, the more clear, yet challenging it becomes. It's not a lacking finale in any way, shape or form, but it's also, perhaps, not personally the preferred one. No matter where it ends, "Source Code" retains exactly the same message, an impassioned, non-preachy plea for people to wake up and stop taking their lives for granted. "It's a really gorgeous day," Sean tells Christina in the film's last minutes. Christina doesn't just half-mindedly reply, but takes a moment to look around. "Yeah," she says. "It is."