The three-part PBS Masterpiece miniseries “Mrs. Wilson,” which premieres Sunday, is an entertaining but daunting experience. Heavy on drama but light on action, the piece methodically deconstructs a widow’s reckoning of her late husband when all of his deceit comes crashing down around her after he’s gone. Every time she finds out something horrible about him – and there’s a lot – we aren’t privy to his actual actions, just her pained and difficult-to-watch reaction.

But if you’re looking for a masterful, five-stages-of-grief kind of reactor, Ruth Wilson — here playing a a fictionalized version of her own real-life grandmother — is your woman. Spellbinding as Alison Wilson, the actress makes us ache for this secretary who thought she truly knew the love of her life Alexander “Alec” Wilson. That is until he died, and then she discovered that he had multiple wives and families.

Iain Glen (“Game of Thrones”) is equally compelling as Alec and the chemistry between them, shown through flashbacks, is intoxicating and undeniable. The two met and fell in love during the start of World War II which only intensifies their May-December courtship. With Wilson telling her own family’s story here, there’s an apparent bias in the portrayal of Alison and Alec’s sons, with Ruth Wilson’s father Nigel (Otto Farrant) coming across as a much more likeable person than his older brother Gordon (Calam Lynch). That shouldn’t make for awkward holiday gatherings, right?

There are also elements of espionage and intrigue, with Alison Wilson and her sons never really finding out how much of a spy Alec was. Making matters more complicated in the film and in real life is the fact that MI5 and MI6 won’t release the files they have on Alec, who also wrote fictional spy novels in his spare time. But because Alec did work for the British government in various capacities, it is hard to decipher which of his tales were real and which ones were fabrications.

Although Alec was an indisputable bigamist, there are even questions about at least one of his marriages and whether or not the union was part of a covert operation. Such murky details will haunt the viewer and continue to perplex Alec’s descendants. The mysterious details behind “Mrs. Wilson” draw you in, but are secondary to the program’s amazing acting. Not only are Wilson and Glen terrific, but scene stealers Fiona Shaw (“Killing Eve”) and Anupam Kher are brilliant as ancillary characters from Alec’s secret service circle.

Take away these transcendent performances and “Mrs. Wilson” is a glorified Lifetime movie. In fact, the producers behind “Mrs. Wilson” should’ve borrowed a trick or two from Lifetime and made the miniseries at least one hour shorter. If they’d cut out every scene where someone tells Alison that Alec was a “good man” – this could be a drinking game, it happens so frequently – the writers and producers could’ve erased at least 25 minutes from the series’ run time.

But in the end, Masterpiece doesn’t do quick jaunts. This is an epic story about one woman’s arduous evolution when her 20-year marriage dies with the stranger who made her a wife while simultaneously giving the job to a few others as well.

TV Review: ‘Mrs. Wilson’

Cast: Ruth Wilson, Iain Glen, Keeley Hawes, Anupam Kher, Fiona Shaw Executive Producers: Neil Blair, Rebecca Eaton, Ruth Kenley-Letts, Lucy Richer, Ruth Wilson