Captain Frye is one of General Frank Hummel's men. Specifically, one of the insane, trigger-happy ones who are in favour of launching rockets filled with deadly VX gas on San Francisco.
Even after Hummel decides not to do so, Frye and his partner-in-slime, Captain Darrow, decide to go through with the scheme anyway. However, thanks to the covert efforts of ex-British agent John Mason and FBI chemical weapons specialist Stanley Goodspeed, Frye and Darrow are down to only one working rocket.
Goodspeed swipes the guidance chip from this and runs off, stuffing one of the green orbs containing a small amount of VX gas into his pocket for safekeeping, with Frye in hot pursuit, demanding that he return the guidance chip. Goodspeed hides, but when Frye approaches his hiding spot, he tosses the guidance chip out for the Marine to see. Apparently being none too intelligent, in addition to being a bloodthirsty wacko, Frye falls for it and bends to pick up the chip. As he stoops down though, Goodspeed attacks, tackling Frye.
The two men roll around on the ground in a life-or-death struggle. Frye manages to get the upper hand, pinning Goodspeed and strangling him. However, Goodspeed has a little surprise for Frye. Luckily for Goodspeed, the psychotic Marine did not see him put the orb of VX gas into his pocket.
Despite being strangled, Goodspeed is still able to remove the orb from his pocket and stuff it into Frye's mouth. Before Frye has a chance to react, Goodspeed uppercuts him, making him bite down, shattering the orb and filling his mouth with the deadly VX gas. Understandably, Frye releases Goodspeed from his grip and Goodspeed manages to get away and quickly inject himself with the antidote, but Frye is not so lucky.
He begins to froth and foam at the mouth, his skin bubbling and melting off, and, off-screen, he dies a much-deserved, slow, agonizing death as described by Goodspeed earlier in the film.