“Run,” which begins Sunday, hurtles through a number of hairpin twists that it would be wrong to spoil. But the real twist of the series, created by Vicky Jones, is that Ruby and Billy aren’t really running off with each other. They are trying to run off with the 19-year-old versions of themselves, to rediscover the unencumbered youths they once were (the sort who would come up with an escape pact that sounds like the premise of a high-concept cable show).

The actual, adult quasi-strangers they encounter are much more dented with age. Billy has a career as a lifestyle guru that has taken a wrong turn; between that and his slick, easy charm, he may as well be wearing a “Do Not Trust” sign on his forehead.

Ruby’s domestic boredom seems more ordinary, but she proves to be as full of secrets and cons in her own low-key way. (She has a husband at home, played by Rich Sommer, who with his roles as a cheating spouse in “Mad Men” and “GLOW” had already become Hollywood’s designated Bad Marriage Guy.)

Yet when the two meet for the first time, the charge is electric and potent — enough, at least, to get them booked in a roomette on an Amtrak chugging toward Chicago. (“This is unforgivable,” Ruby says, as much from the thrill as from guilt.)

It’s when they hit the rails that the second thoughts hit, and the secrets, and the conspicuous holes in their back stories. Soon the two realize that they’re each on the lam — not with a fantasy partner but with the reality of a person they’ve spent years idealizing. “Before Sunrise” this is not. Acid-tongued and mordant, it’s more like before the fall.