CHICAGO  On a film soundstage here, a tense scene was unfolding, with the actor Lou Diamond Phillips, playing a rogue cop, holding a gun aimed at the head of another actor, who stood tall, unflinching, his face and frame thinner than in his glory days, but still handsome, his hair concealed under a tight-fitting black beret.

“Go ahead, you’ll do me a favor,” said Patrick Swayze in the voice of Charles Barker, an undercover F.B.I. agent with dark secrets, a character the actor later described as “someone who’s dying inside, someone with a death wish.”

There was no heavy-handedness in the line of dialogue, intended or accidental. Nothing about the scene  one of the many Mr. Swayze is filming on location here in the course of making a new police drama called “The Beast”  suggested anything other than that professional actors were at work.

But of course something quite out of the ordinary was taking place. A celebrity film star, who was given a diagnosis of pancreatic cancer less than a year ago, was putting in 12-hour days as the lead in a television series.