Mission to kill (as it says in the opening credits) aka The Phoenix Report (as it says at the end of the film) started out as a straight ahead action film with the promise of a story involving Big Bill Smith chasing a crazed marine across America, but instead it seemed to develop into some sort of drama with a real let-down ending.
In Vietnam, a crack, covert team are trained to kill key figures in the Vietcong. We see two marines taking on Charlie in a hail of bullets when one gets killed and the other captured. Flash-forward to (on-screen caption) 1990 (even though someone later refers to it being the eighties) where Major Miller, whom we're led to believe was the guy we saw getting captured as a different actor, is receiving psychiatric treatment in a mental hospital, where due to his occupation he's being kept away from the public.
Miller escapes, and they send Big Bill Smith after him, and then, well, nothing really of note happens for the rest of the film. I'm not making this up. Smith goes around talking into a Dictaphone, doing a bit of PI work and acting menacing, but you've got to believe me when I say that the escaped mental patient doesn't go crazy and start gunning people down, and Smith doesn't turn out to a covert evil government machine or anything. He just looks for the mental patient, the mental patient has a bit of drama with his missus, there's a slight brawl, and the film just kind of ends on a note that'll have you thinking "Why did they bother with all the proceeding guff?"
I reckon the Vietnam footage comes from a different film. A Mission to Kill is kind of quirky in a way (the deaf tramp, the girlfriend's drug addiction) but if there's no action and no pay off, why bother in the first place? Don't ask me - ask Bill Smith - he wrote the story!