Phoebe Waller-Bridge knows how to quit while she’s ahead.

Friday marked the stateside return of “Fleabag,” her dry-witted Amazon series that, following its acclaimed first season, almost didn’t get a second. It didn’t really need one, given the English auteur’s affinity for concise storytelling. The six half-hour episodes that debuted back in 2016 — two years before Waller-Bridge’s popular BBC America series “Killing Eve” — painted such a robust portrait of a droll, self-destructive woman that they felt sufficient on their own. (Amazon founder Jeff Bezos owns The Washington Post.)

And yet the second season, greenlit two years ago, has been deemed “unmissable,” “profound” and “a minor miracle” — a testament to critics’s fondness of Waller-Bridge, who insists that this is the last we’ll ever see of the irreverent character. Whereas the first season uncovered how the sudden death of her best friend led Fleabag to spiral, the second explores what happens when she finally meets someone whose emotional turmoil complements hers.

There’s a snag, of course — this is “Fleabag” we’re talking about. The love interest happens to be a man of the cloth, referred to only as the Hot Priest (Andrew Scott, known for his maniacal portrayal of Jim Moriarty in the BBC’s “Sherlock”). Fleabag struggles to keep her distance, while the charming priest tries to reconcile his feelings with his sworn celibacy.

“They’re the characters I root for the most, because I can relate to that,” Waller-Bridge said in a recent phone interview. “It shows that someone is reaching for something good, if they’re testing themselves all the time."

Waller-Bridge, who in addition to “Killing Eve” created the bingeable Channel 4 sitcom “Crashing,” infuses her shows with caustic humor, employed by characters as flawed as they are unpredictable. Viewers are in for a shock (or several) each time they hit play on any one of her shows.

“Fleabag” grew out of a comic monologue Waller-Bridge wrote several years ago, and that she has since brought to both New York and London’s West End. She described the character, who owns a guinea pig-themed cafe in London, as an “amplified version of my own cynicism at the time, which is somebody who really believed that her main value in the world should be measured by how attractive she was.” Fleabag channels her insecurities into “an honesty and a brashness” that Waller-Bridge hadn’t often seen onstage or screen. This led many to categorize her as an antiheroine, a characterization the series, especially in its second season, slowly unravels.

The Hot Priest, for all the moral ambiguity that exists in his relationship with Fleabag, brings out a more sincere side of her that we haven’t seen before. Waller-Bridge said she toned down his priestliness to ground the character in reality. He swears and drinks and encourages Fleabag to let her guard down, as we encounter in the season premiere at a tense dinner they attend with her widowed father (Bill Paterson) and terrible godmother (Olivia Colman), whose upcoming wedding the priest will officiate, as well as Fleabag’s uptight sister, Claire (Sian Clifford), and her scumbag husband, Martin (Brett Gelman).

When she initially sat down to write “Fleabag,” Waller-Bridge said, the first scene that came to mind wound up opening the second season. It’s been a year since the events of the first season’s finale, when Fleabag and Claire got into a blowout fight after Claire, citing her sister’s past transgressions, refused to believe that Martin tried to kiss Fleabag. Fleabag now treats a bloody nose in the restaurant bathroom.

“I’m constantly working out who these characters are while I’m writing them, hoping they’ll surprise me as they come out,” Waller-Bridge said. “I’ll reveal the big thing about this person, and backtrack from there. It’s quite haphazard, depending on which character I’m writing as well.”

We go on to learn that Fleabag’s injury stems from a particularly nasty confrontation with Martin, who had been spouting insults about a miscarriage he believed Fleabag endured (when she had actually been covering for Claire). Though Waller-Bridge has made a name for herself exploring the inner workings of the female psyche — and has professed a love of writing the volatile Fleabag and more predictable Claire, whose relationship evolves throughout the series — she named Martin as one of her favorite characters to explore this season.

“He’s such a different part of my brain that I could tap into . . . that, like, a---hole bit of my brain,” she said. “It’s always a challenge because I do want the audience to feel something other than disgust and hatred for him as well. I always try to take [my characters] as far away from that at the end.”

This explains the disquieting allure of Oksana “Villanelle” Astankova (Jodie Comer), the coldblooded yet playful Russian assassin at the center of “Killing Eve.” She’s one of the best in the business and develops an obsession with Eve Polastri (Sandra Oh), an American woman working in British intelligence. The feeling is mutual. The resulting cat-and-mouse pursuit stretches past the first season and into the second, which premiered last month, giving creator Waller-Bridge and Season 2 showrunners Emerald Fennell and Sally Woodward Gentle ample opportunity to dissect the women’s motivations.

The psychological drama, which has earned both of its actresses accolades, stunned viewers in its first season when Villanelle slips into Eve’s home. The two share a meal, with Eve gripping a knife for safety. While afraid, Eve “intuits things about Villanelle,” Waller-Bridge said. “She can see right through her."

“The idea of power, and each of them having a different superpower, really made it easier to measure the changes between them,” Waller-Bridge continued. “Eve’s superpower is that she’s a super empath. She feels things very deeply and sees through people very quickly. Villanelle is the exact opposite, with her psychopathic traits. What became really fun was working out which one had the upper hand, and why.”

Villanelle begins to exhibit a vulnerability in the second season, highlighting Waller-Bridge’s tendency to dismantle viewers’s notions of an established character. It’s a skill that probably will prove helpful to the offbeat writer, who, in addition to landing a series order from HBO for a comedic thriller, is set to polish the script of the upcoming James Bond film at the behest of star Daniel Craig himself.

“I could bring some fun and darkness, what I’m always trying to reach for in everything,” Waller-Bridge said. “Something frightening, something sexy. A little bit of wit.”

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