context: Walker (Lee Marvin) works together with his friend Mal Reese (John Vernon in his first major role) to steal a large amount of cash from a courier transporting funds for a major gambling operation, with the deserted Alcatraz island as a drop point. Reese then double-crosses Walker by shooting him, leaving him for dead. Reese also makes off with Walker's wife Lynne (Sharon Acker).
  Walker recovers. With assistance from the mysterious Yost (Keenan Wynn), who seems to know everything about everybody involved in the heist, Walker sets out to find Reese, take his revenge, and recover the $93,000 he is owed. Reese used all of the money from the job to pay back a debt to a crime syndicate, "The Organization", and get back in its good graces.
  With memories of happy times together, Walker goes to Los Angeles to pay back his wife and his best friend for their treachery. He bursts in on Lynne and riddles her bed with bullets, just in case Reese is in it. A distraught Lynne tells him she no longer wants to live, then takes an overdose of pills.
  Walker is told a car dealer named Stegman (Michael Strong) might know where Reese can be found. Posing as a customer, he takes Stegman for a wild ride in one of his new cars, smashing the car and terrorising him, until Stegman reveals where Reese is living. He is told Reese has now taken up with Walker's sister-in-law, Chris (Angie Dickinson).
  Breaking in on Chris, he learns she actually despises Reese, and had considered Walker the best thing ever to happen to her sister.
  Willing to help in any way, Chris agrees to a sexual tryst with Reese, inside his heavily guarded penthouse apartment, just so she can gain access and unbolt a door for Walker. Walker ties up some men in an apartment across from the penthouse, and has a call made to police to report a robbery, creating a diversion that enables him to slip into the penthouse.
  With a gun to Reese's head, Walker persuades him to give up the names of his Organization superiorsâCarter, Brewster, and Fairfaxâso he can make somebody pay back his $93,000. Reese says he'll help Walker. Walker attempts to quickly move Reese to the balcony by yanking on the blanket Reese has wrapped around himself. However, whether due to too much force or Reese attempting to get away from Walker, Reese is flung over the railing of the balcony, and Walker watches as a naked Reese plunges to his death on the street below.
  Walker next confronts Carter (Lloyd Bochner) for his money, and Carter promises to pay. Carter gives a package, which he says contains the $93,000, to Stegman. When Stegman questions why he was chosen for this task, Carter says it's because he knows what Walker looks like. In fact, Carter is trying to set Walker up.
  Stegman arrives at the destination (the Los Angeles River) and is standing out in the open on the river's dry concrete bed. Carter has followed to watch surreptitiously. Just as Carter is feeling comfortable, Walker jumps out from behind him, surprising Carter. Walker puts Carter in a choke-hold, telling him to go get the package from Stegman and bring it to Walker.
  Unbeknownst to Stegman, a hit man (James Sikking) with a high-powered rifle has been posted hundreds of yards away, to kill Walker when the transfer takes place. Carter knows the hit man is aiming his rifle at that very second, and as Stegman tries to understand why Carter is there, Carter frantically waves his arms, hoping that the hit man will see he is not Walker.
  Instead, the hit man fires, and Carter drops. As the reality of the situation becomes clear to Stegman, he tries to escape by walking quickly across the vast, desolate stretch of the river bed, only to also be shot dead as well.
  While the hit man packs up his weapon on the bridge, Walker cautiously goes over to the package, and when he rips it open, discovers that it is packed with nothing but paper.
  Yost takes Walker to a home belonging to Brewster (Carroll O'Connor). Walker visits Chris in her apartment, which was trashed by the Organization. He brings her with him to Brewster's home, claiming she will be safer with him than by herself.
  As Walker waits for Brewster to return, an angry Chris starts slapping and pounding Walker, over his apparent disinterest in her. As Chris continues to punch him, Walker regards her impassively, not defending himself. After Chris hits Walker over the head with a pool cue, the two become entangled beneath the pool table, and their anger turns passionate. They make love.
  The following morning, Brewster comes home and is ambushed by Walker, who demands his money. Brewster insists no one will pay. Walker forces Brewster to make a phone call to the Organization to get his money. Brewster speaks with a Mr. Fairfax, telling him that if they do not pay the money, he is going to be shot, but Fairfax refuses to pay, saying, "Threatening phone calls don't impress me."
  Walker then shoots the phone.
  Brewster says that they can still get him the money up in San Francisco through "The Alcatraz Run," in which large sums of money change hands. "The drop has changed, but the run is still the same," explains Brewster.
  They travel to Fort Point in San Francisco. Walker does not trust Brewster. As Brewster stands in the open space of a courtyard, we see Walker, high above and hidden in the darkness, refusing to show himself.
  Brewster receives the money by a courier in a helicopter. The hit man is also in the darkness with his rifle. He shoots Brewster, who falls to the ground, thinking Walker has shot him.
  Yost emerges from the shadows, telling him it was not Walker who shot him. Brewster calls out to Walker, "This is Fairfax, Walker! Kill him!"
  Yost/Fairfax thanks Walker, still hiding in the shadows, for eliminating his dangerous underlings, telling him, "Our deal's done, Walker. Brewster was the last one." Fairfax then offers Walker an enforcer job, claiming he has looked for a man like Walker for years. Walker stays hidden and does not answer.
  The hit man is about to pick up the package containing the money, but Fairfax tells him to leave it. Walker remains unseen as the two men leave.
question: Who double crosses the man?
answer: Fairfax