Based on the 1973 novel by Lois Duncan, I Know What You Did Last Summer was adapted to the small screen — here’s your guide to the cast and characters appearing in the new Amazon Prime series. Most viewers probably know the series’ premise thanks to the 1997 film of the same name starring Sarah Michelle Gellar, Jennifer Love Hewitt, Freddie Prinze Jr., and Ryan Phillippe. The Amazon series follows a very familiar story, but one with several twists and character dynamics that allow it to stand apart from the film (and its sequels).
Boasting a large cast of characters, I Know What You Did Last Summer sees a group of teenagers in a fatal car accident after leaving a graduation party. Rather than reporting the incident to the police, they collectively decide to do away with the body, coming up with a story about what happened to cover their tracks and ensure they’re never caught. Suffice it to say their past comes back to haunt them a year later when they begin receiving threats, a shadowy killer who knows what they did the summer before stalking them, clearly out for blood and revenge.
To change things up from the film, Amazon’s I Know What You Did Last Summer includes a host of new characters with different backstories and relationships. Here is every major and supporting character in the show and the actors behind their portrayals.
Madison Iseman As Lennon & Allison
Madison Iseman pulls double duty as Allison and Lennon, twins who are wildly different from each other. Allison is more of a recluse, distant from others and who is convinced that the only person who ever loved her is her mother, who died by suicide years prior to the start of I Know What You Did Last Summer. Lennon, on the other hand, is the stereotypical wild child. She parties a lot and takes plenty of drugs. Iseman has starred in a plethora of films, including Annabelle Comes Home, Goosebumps 2: Haunted Halloween, Jumanji: Next Level, and Fear of Rain.
Ezekiel Goodman As Dylan
Ezekiel Goodman plays Dylan in the Amazon series I Know What You Did Last Summer, one of Lennon’s longtime friends and whom Allison has had a major crush on for years. Dylan keeps to himself mostly, especially following the fatal accident. Goodman has starred in the TV miniseries Rat Bastard, playing a character named Bad Andrew. The actor has also been in the 2021 film Dragonfly and two short films, A Shore and Drive-In Date.
Brianne Tju As Margot
Brianne Tju plays Margot, a friend of Lennon and Dylan’s. Margot is a social media influencer and is always online, often encouraged to do so by her mother. Tju has starred in Hulu’s Light as a Feather, The Crooked Man, and the upcoming films Three Months and The Cow. Tju is also a TV guest star staple, having appeared in episodes of Grey’s Anatomy, Chicago P.D., iZombie, and Scream: The TV Series.
Ashley Moore As Riley
Ashley Moore plays Riley, the fifth member of the friends group. Riley is closest with Lennon and Dylan. It’s also hinted that she harbors feelings for Dylan. Moore has been featured in a variety of projects, including in Drake’s music video with Majid Jordan, “Hold on, We’re Going Home,” and Popstar: Never Stop Never Stopping, and the pilot for Alone Together.
Sebastian Amoruso As Johnny
Sebastian Amoruso plays Johnny, Margot’s best friend and one of the teens who is in the car when they hit someone on the night of their high school graduation. Amoruso doesn’t have many credits to his name and Amazon’s I Know What You Did Last Summer is his biggest role yet. The actor previously starred in two episodes of the crime series Solve.
Bill Heck As Bruce
Bill Heck portrays Bruce, Allison and Lennon’s father. Bruce runs the local diner and has an on-again/off-again relationship with Lyla, the Wai Huna police chief. Elsewhere, Heck most recently starred in Netflix’s Locke & Key, playing Rendell Locke. The actor has also been in I’m Your Woman, the neo-noir crime film starring The Marvelous Mrs. Maisel’s Rachel Brosnahan, The Ballad of Buster Scruggs, and guest starred in TV shows like The Alienist, Bluff City Law, Ray Donovan, Sleepy Hollow, The Americans, The Leftovers, and had a minor role in The Amazing Spider-Man 2.
Fiona Rene As Lyla Kalei
Fiona Rene plays Lyla, the aforementioned police chief who is working overtime to find the killer and keep the small community calm after a string of murders. Rene is most notable for playing Detective Kara Lee in Stumptown, which was renewed for season 2 before it was cancelled by ABC shortly thereafter. Rene has also guest starred in series like Grey’s Anatomy, Jane the Virgin, and L.A.’s Finest. She’ll next be seen in the film Patsy Lee & The Keepers of the 5 Kingdoms.
Cassie Beck As Courtney
Cassie Beck portrays Courtney, Riley’s often neglectful mother. Courtney is especially protective of her neighbor, who many begin to suspect might be the killer. Beck has appeared in episodes of HBO’s High Maintenance, Chicago Med, Pose, and Elementary.
I Know What You Did Last Summer Supporting Cast & Characters
Chrissie Fit as Kelly Craft - Kelly Craft is Courtney and Riley’s neighbor, and the ex-wife of the high school coach. Chrissie Fit’s most notable role is as Flo in Pitch Perfect 2 and Pitch Perfect 3. Fit also voiced Princess Valentina in the animated series Elena of Avalor, and had a multi-episode guest starring role in Awkwafina is Nora from Queens.
Spencer Sutherland as Dale - Dale works at the Snak ‘n Stuff restaurant. He is an acquaintance of the core friends group who they believe may have seen something the night of the accident. Spencer Sutherland has been in Afterlife of the Party and the series Vote for Love.
Brooke Bloom As Clara - Brooke Bloom plays Clara, a mysterious figure who lives near the cave where many have lost their lives. Bloom has appeared in the romcom He’s Just Not That Into You, the Adam Driver and Scarlett Johansson drama Marriage Story, and Extremely Loud & Incredibly Close. Bloom has also guest starred in TV series like The Sinner, Homecoming, New Amsterdam, and Evil.
Sonya Balmores as Margot’s mom - Margot’s mom is the one who throws the graduation party and who is deeply invested in her daughter’s influencer life. Sonya Balmores played Aurann Marvel’s Inhumans series. She has guest starred in a plethora of shows including Lucifer, Roswell, New Mexico, Magnum P.I., and FBI: Most Wanted.
Eric William Morris as Officer Cruise - Officer Cruise is Lyla’s subordinate and who believes Kelly Craft is the prime suspect in the killings. Eric William Morris has had guest starring roles in Blue Bloods, Mindhunter, The Marvelous Mrs. Maisel, Quantico, and FBI.
Duncan Kamakana as Coach Eric Kraft - Eric Craft is a high school sports coach and the ex-husband of Kelly Craft. Duncan Kamakana has a slim filmography, having appeared in guest roles on Hawaii Five-0 and Magnum P.I.
Dann Seki as Harold - Harold plays the chef at Snak ‘n Stuff, the restaurant Bruce owns in I Know What You Did Last Summer. Dann Seki has appeared in The Informant! (which starred Matt Damon) and in episodes of Hawaii Five-0, Lost, and Baywatch.