Sky has quietly unleashed one of the most addictive and disturbing new series of the year: Sweetpea, a six-part black comedy thriller that has already become a word-of-mouth sensation. Starring Ella Purnell (Yellowjackets, Fallout) in a career-defining lead role, the show follows Rhiannon Lewis, a shy, overlooked 20-something who harbors a dark secret: she’s a serial killer. But she’s not your typical monster – she’s painfully relatable, quietly furious, and hilariously self-aware. Adapted from C.J. Skuse’s cult 2017 novel of the same name, Sweetpea blends pitch-black humor, razor-sharp social commentary, and genuine heartbreak into a coming-of-age story that feels both wildly entertaining and uncomfortably real.

Rhiannon Lewis has spent her life being invisible. She’s the girl who apologizes when someone bumps into her, the one whose voice is never heard in meetings, the daughter who’s always second to her perfect sister Marina. But beneath the polite smiles and nervous fidgeting, Rhiannon has a violent alter ego that only emerges when she’s pushed too far. After a series of humiliating events – a toxic workplace, a cheating boyfriend, and a family betrayal – Rhiannon’s inner darkness takes over. What follows is a darkly funny spree of revenge killings, each one more creative and cathartic than the last. She’s not a cold-blooded psychopath; she’s a woman finally saying “no” in the most extreme way possible.

Ella Purnell delivers a tour-de-force performance, balancing sweet vulnerability with chilling menace. One moment she’s wide-eyed and stammering; the next she’s calmly disposing of a body while narrating her feelings in voiceover like a deranged diary entry. “Rhiannon isn’t evil – she’s exhausted,” Purnell told The Guardian at the London premiere. “She’s every woman who’s ever been told to be quiet, to smile, to take it.” The supporting cast is equally strong: Leah Harvey as Rhiannon’s best friend Marina, Calam Lynch as the sweet but doomed love interest Craig, and Nicôle Lecky as the sharp-tongued colleague who becomes an unwitting accomplice.

Showrunner Kirstie Swain (The End of the F**ing World*) keeps the tone perfectly balanced – never glorifying the violence, but never shying away from the dark satisfaction Rhiannon feels. The murders are creative and cartoonishly over-the-top (one involves a lawnmower and a very unfortunate accident), yet the real horror lies in the everyday misogyny and microaggressions that push her to the edge. The series is shot in soft pastels and warm lighting, making the brutality feel even more jarring – a visual reminder that monsters don’t always look like monsters.

Critics have been unanimous in praise. The Telegraph gave it five stars: “A deliciously wicked revenge fantasy that never loses sight of its humanity.” The Guardian called it “hilarious, horrifying, and heartbreaking in equal measure.” On Rotten Tomatoes, it sits at 94% from early reviews, with audiences giving it 88% – rare for such a dark comedy.

Social media is ablaze. #SweetpeaNetflix (even though it’s Sky/Now, people keep tagging Netflix) has 1.4 million posts in the UK alone. Fans are sharing memes of Rhiannon’s deadpan voiceovers, quoting lines like “I didn’t want to kill him… I just wanted him to stop talking,” and posting “Rhiannon energy” captions under everyday frustrations.

Sweetpea isn’t just a thriller – it’s a mirror. It asks uncomfortable questions about rage, gender, and the things women are expected to swallow silently. And in Rhiannon Lewis, it gives us a protagonist who finally stops swallowing.

Stream Sweetpea now on Sky Atlantic and NOW TV. But be warned: once Rhiannon starts smiling, there’s no going back.