‘The Ex-Wife’ blasts the gaslight flame in creepy psychodrama

“The Ex-Wife” tells a sordid tale of gaslighting writ large — but takes the familiar “psychological thriller” in a twisty turn that sets it apart from its genre bedfellows.

The four-part series, premiering Aug. 10 on streamer BritBox and based on Jess Ryder’s book of the same name, features an English cast familiar to the US TV audience: Tom Mison (Fox’s “Sleepy Hollow”), Janet Montgomery (NBC’s late, great “New Amsterdam”) and Céline Buckens (“Free Rein,” “Warrior”).

It’s a trope-laden drama with just enough surprises to keep viewers interested as it barrels along to a booming finale.

The series opens with a meet-not-so-cute between media executive Jack Warrington (Mison) and graphic designer Natasha (“Tasha”), who’s riding her bicycle to work on a busy street when a speeding Jack plows into her with his car.

She’s not seriously injured, save for a few bumps and bruises, including a scraped-up arm, and Jack — sheepish, apologetic and wanting to avoid “a scene” — promises to pay for her smashed-up bike. He takes her back to his ginormous home in a leafy London suburb to tend to her arm and soothe her frazzled, dazed nerves.

Jack is obviously well-off and is living alone; turns out he’s in a “trial separation” from his wife, Jen (Montgomery), and, after a bit of flirting, asks the much-younger Tasha out for dinner.

One thing leads to another and in 3 … 2 … 1 there’s the gratuitous semi-blurry, soft-focus sex scene. In short order they marry, she gets pregnant and they welcome a baby girl, Emily.

They’re destined to live happily ever after, but the series is titled “The Ex-Wife” — and when Jen starts showing up and acting extra-chummy with Jack, who seems to welcome the attention, let’s face it: how can he miss her if she won’t go away?

Tasha is initially semi-indulgent of Jen’s omnipresence but, before long, it starts to wear thin, even though Jack repeatedly reassures her she’s the only woman in his life (though he’s caught in a lie or two or three).

Jack’s behavior triggers alarm not only in Tasha but in her pal, Sam (Jordan Stephens); they had a one-night stand pre-Jack but he’s obviously in love with Tasha and doesn’t trust her new husband — who takes an awful lot of “business trips to New York” — as far as he can throw him, and the feeling is mutual.

Mison, Montgomery and Buckens are excellent as the cad, the creepy ex and the too-young, fragile second wife, but those roles are, eventually, all turned on their heads as the arc of “The Ex-Wife” slowly starts to evolve and the characters’ true colors begin to shine through in surprising fashion.

It’s not pretty, by any stretch, but that’s the point, and your expectations will not only be quashed, one by one, but likewise heightened by several plot contrivances that, on the surface, seem hackneyed (but really aren’t once all is said and done).

The series coda strikes a somewhat silly note in that horror-movie kind of way, but doesn’t take anything away from an absorbing drama that will question your expectations nearly every step of the way.