In a time when perfectly understandable conspiracy theories abound to explain the chaos of contemporary history, the thriller naturally flourishes. Since it often shows an innocent person thrust into a dangerous situation by the random hand of fate, it suggests that anyone, no matter how harmless or anonymous, may be vulnerable to the sinister action of some external force.

That menace varies according to the time and place, but it almost invariably expresses an appropriate anxiety, which, depending on the particular era, includes the fear of another world war, the fear of nuclear annihilation, the fear of terrorist attacks, all of them, however genuine, encouraged and exploited by political leaders. In recent decades the thriller responds to the generalized cultural paranoia, based on the actions of government itself - the actual and imagined conspiracies of the FBI, the CIA, the NSA and all the other alphabetical entities documented as threats to their own people.

The basic mystery in the new thriller "Edge of Darkness" develops from a single inexplicable incident into a familiar revelation of the power and extent of a collusion between government and industry to control wealth, information, and people. It opens with some startling moments, first showing three corpses quietly popping up on the surface of a scenic river bathed in moonlight, then soon explodes into sudden violence with the shotgun slaying of a Boston detective's daughter, who dies in her father's arms. The detective, Tom Craven (Mel Gibson), and his colleagues initially believe the shooter aimed for him, and proceed to investigate his past cases, but Craven's own pursuit of the murderer leads to something much more complicated than an assassination.

As he follows the evidence, he begins to learn about his daughter's job with a nuclear research laboratory, which apparently exposed her to radiation sickness. He questions her recalcitrant boyfriend, who reveals more information about Northmoor, the corporation that employed them both; when he visits Northmoor itself, the CEO smoothly stonewalls his inquiries. That encounter leads to a series of violent confrontations, car chases, shootings, and the revelation that the killing was no mistake, that Craven's daughter really was the intended target, and that Northmoor deals in a complicated scheme to produce nuclear weapons.

Craven uncovers one of the most convoluted conspiracies in recent film, a serpentine trail that runs through the Department of Defense, the CIA, major corporations, and some unnamed foreign governments. Prying into his daughter's murder touches off a series of killings orchestrated by a mysterious group of government operatives working with a powerful United States senator. Whatever his skills and experience and the depth of his tenacity and passion, as the movie shows, the Boston cop doesn't stand a chance against that collection of ruthless and utterly amoral killers.

Aside from the urgent pace and nonstop violence of the investigation, "Edge of Darkness" develops its emotional content from the relationship between the detective and his daughter. Throughout the picture Gibson recalls moments from her childhood, speaks to her, dreams of her; his love for Emma motivates all he does, turning him into an unstoppable force, a man who cares about nothing but the truth and his revenge. The combination of two different forms, the conspiracy thriller and the revenge thriller, create an energetic dialectic and a credible explanation for all of Craven's actions.

Acting rather more hysterically than in most of his previous parts, Mel Gibson of course occupies the foreground of the movie, frantically chasing down leads, beating up antagonists, shooting a number of bad guys, driven always by the memory of his daughter (the script offers no hint of a wife, dead or ex-). As an ambiguous figure who connects all the various threads, Ray Winstone, however, provides the most engaging performance; he makes his character, a professional assassin, a thoughtful, sensitive, even admirable figure with a philosophical turn of mind.

His final gestures, coupled with the odd, rather sentimental transcendence of the film's conclusion, in effect explain the unusual solution to the tension of conspiracy and revenge. He sums up the essential melancholy of "Edge of Darkness" in a conversation with the men behind all the manipulation, betrayal, and death, uttering what could be the motto of the movie: "We're all terminal."