In the opening shot of director Ray Lawrence’s “Lantana,” the camera pans across a thick, tangled woodland bush — delicately probing the dense, mysterious uncertainty of the unruly natural world. The sound of buzzing bees mingles with the windy rustling of branches and the distant, scratchy eruption of a water hose. As these sounds and images lure the viewer into a comfortable sense of security, a rotting foot, followed by the remainder of a decaying corpse, enters the frame.

In just 30 seconds, “Lantana” has successfully created and destroyed the viewer’s expectations. Yet the greatest surprises begin as the film slowly unravels its story, a brilliantly paced, fully realized venture into uncharted territory. At once an enigmatic murder mystery and a heated domestic drama, “Lantana” investigates how trust can both revitalize and suffocate a fragile relationship.

Lawrence examines these painful emotional realities through the intersecting fates of four very unique married couples living in the same city in Australia. Leon (Anthony LaPaglia), a smart, hardworking detective, both loves and feels trapped by his quietly tortured wife Sonja (Kelly Armstrong), who yearns for more passion and complexity in her marriage. Leon seeks solace in an exclusively sexual affair with lonely Jane (Rachel Blake), a subdued dancer contemplating reconciliation with her trusting but distant husband. Jane longs for the family life of stability and happiness reflected in the blissful contentment of her young neighbors, Nick (Vince Colosimo) and Paula (Daniella Farinacci).

Meanwhile, Sonja’s emotionally wounded therapist Valerie (Barbara Hershey), grapples with the loss of her young daughter as well as with the wounds the death has left on her disintegrating marriage with the tortured but externally steeled John (Geoffrey Rush).

When one character goes missing in the Australian woods (you will have to see the movie to find out who), each character must grapple with new issues while still confronting their unresolved problems.

“Lantana” is electrifying in its simplicity: the script so subtly invests each character, each relationship, and each confrontation with the perfect tone of emotional realism that the movie needs no elaborate composition to succeed. As previously unintroduced characters randomly meet, they reflect their desperation onto each other, creating new intricacies in their emotional journeys.

By remaining so true to the characters it creates, “Lantana” is able to infuse mystery and intrigue into a human drama without the viewer questioning its validity as a natural character study. In fact, the mystery tests these relationships in new, interesting ways, heightening the tension: as one couple bends under the weight of a marriage in which too much trust suffocates, another relationship attempts to mend itself by confronting an absence of trust.

“Lantana” also features one of the finest ensemble casts of the year. LaPaglia plays Leon with a toughness that makes his inability to understand his own decisions extraordinarily touching; Hershey brilliantly unveils a grief too powerful to be palpable; and Rush, who overacted in histrionic spectacles like “Les Miserables” and “Quills,” gives one of his finest performances, as a man afraid of the destructive power of his own pain.

Despite the uniform excellence of these established performers, it is Australian unknown Kelly Armstrong, as the yearning Sonja, who gives the film its heart. Armstrong gives new meaning to the middle-aged need to avoid routine — the scene in which Sonja contemplates a fling with a much younger man at a dance club is touching because Armstrong so convincingly portrays a woman willing to forgo humiliation to alleviate her longing.

While the film’s examination of the harsh realities and private pains of the human experience are both mesmerizing and unsettling, its greatest surprise comes in its final optimism. After Leon accidentally bumps into a passing jogger, the burly man collapses sobbing in his arms. A friend later explains to the disgusted Leon that “sometimes people just cry.” Yet by the end, the film offers an explanation and a resolution to these tears. For a movie that examines the painful complexity of relationships it’s a comforting reminder that people cry for a reason.