The addition of the star to Only Murders in the Building has, unsurprisingly, made the show’s new season much more worth watching.

Only Murders in the Building is easy to watch. Each season follows Charles (played by Steve Martin), Oliver (Martin Short), and Mabel (Selena Gomez), true-crime podcasters who solve murders in the Arconia, the titular building in which they live. Every episode mines comedy from the trio’s generational differences and explores how their unusual shared hobby bolsters their equally unusual friendship. The stakes are low, but the joke density is high, and the twists are always more fun than frightening.

Plus, there’s a seemingly endless parade of recognizable guest stars to keep things light. Charles, Oliver, and Mabel never fail to encounter the most wonderfully kooky personalities during their investigations: fellow Arconia tenants, forgotten relatives, neighborhood regulars. The series’s first two seasons featured, among many others, Nathan Lane, Tina Fey, Shirley MacLaine, and Sting (yes, Sting), most of whom became suspects in the killings.

Meryl Streep, who joined the show’s starry ensemble this season, just might be the most eccentric guest star yet. Her character, Loretta Durkin, is, unlike Streep, a struggling actress who has lived in the same shabby apartment for decades and finally gets a break by being cast in Death Rattle, a new show by Oliver, who is a theater director staging his Broadway comeback. In almost every scene in which she appears, Loretta is the picture of warmth: her hair in braids, a shawl or cardigan draped around her shoulders, looking the way she did as a little girl (as we see in flashbacks). The show has, in its latest episode, positioned her as its newest primary suspect in the murder of her castmate Ben (Paul Rudd). But Loretta is more than another potentially guilty party being played by a notable name. In Streep’s hands, she helps make Only Murders a show worth watching more closely, and not just for the slow drip of clues or the charm of its lead cast.

Streep plays Loretta as someone simultaneously open and inscrutable, a suspect who makes viewers work to understand why she’d be on the murder board at all. Loretta hated Ben, but she’s quick to apologize for speaking ill of the deceased. She’s sweet and scatterbrained, exuding the energy of a loving aunt; at the same time, she offers glimpses of a more devious side that could be read as further proof of her quirky nature or something more sinister. In a standout scene from this week’s episode, she invents several scenarios about why she and Oliver didn’t cross paths until so late in her career, each one more violent than necessary. (She describes getting her ponytail stuck in the subway doors on the way to an audition, and passing out after being drugged by the Broadway star Bernadette Peters.) Already enamored with her, Oliver is delighted by the bit. And from the audience’s perspective, perhaps Loretta really is just flirting, high off her and Oliver’s shared joint—or perhaps she’s wilier than she seems. That’s Streep’s trick: She makes Loretta apparently easy to read—until she’s not.

Of course, claiming that the multi-Oscar-winner Streep is outstanding in her role—one that’s been evidently pivotal from the season’s opening scene – is not exactly a groundbreaking observation. But consider how previous guest stars have been deployed on the show. Some, such as Sting, have played outsize versions of themselves, using their celebrity as the punch line. Others, suc as Rudd as this season’s victim, portray deliberately and hilariously cartoonish characters, helping the mystery feel far from grim.

Streep could have done much less to embody Loretta. Instead, the actor both pokes meta fun at her own reputation as a performer—Loretta can’t help but do impeccable accent work—while deepening the part. In Episode 3, she infuses a solo ballad with profound vulnerability; in this week’s episode, she shows how Loretta can be both confident and fragile in a single scene as she tells an adorable anecdote from her childhood before lamenting how unsuccessful she’s been in her career so far. Streep is obviously having fun playing the role, but she’s also ensuring that her character is not just a ball of peculiarities. Informed by dashed hopes and unmet desires, she’s proof that youthful dreams and habits can be hard to outgrow.

Sometimes, casting a major star can be a distraction. Adding Streep to the second season of Big Little Lies, for instance, kept the series relevant and drew eyeballs, but it failed to save the show from devolving into an overwrought, convoluted drama. In Only Murders, however, Streep’s presence and performance only underline the show’s strengths: Loretta is a tricky suspect to decipher, a pivotal addition to the central trio’s dynamic, and evidence that the series—after a lackluster second season—can still offer complex character studies amid whodunit-related gags. Only Murders has, in other words, given Streep a role worthy of her talent—and, as a result, given its viewers a season that’s as compelling as it is comforting.