The Slow Horses Season 7 teaser has sparked speculation about a major storyline from Mick Herron's novels finally making its way to the screen.Apple TV's Emmy-winning spy-thriller series recently wrapped its sixth season on a shocking cliffhanger, and fans are already anticipating the upcoming season. Esquire shared a teaser for Slow Horses Season 7, which will adapt Herron's eighth book in the Slough House series, Bad Actors. According to Men's Journal, the official synopsis for the upcoming season reads as follows:“In Season 7, Lamb and his Slow Horses are on the hunt to find and neutralize a mole at the heart of the British Government before they can bring down the state.”Naturally, Lamb and the Slough House agents will be swept into yet another conspiracy in Season 7. But the teaser hints that Shirley Dander's (Aimee-Ffion Edwards) story in Bad Actors could become relevant to the upcoming season.Marked by her severe anger management issues, drug addiction (specifically cocaine), and a history of punching her superior officer, Shirley remains one of the most prominent MI5 agents, and her book story might come to life in Season 7, as Lamb sends her to rehab.Disclaimer: The following article contains spoilers for Mick Herron's Bad Actors. Reader discretion is advised.Slow Horses Season 7 might bring Shirley to the forefrontThe Slow Horses Season 7 teaser suggests that Shirley might get a spotlight in the upcoming entry. The teaser offers glimpses of Shirley, as she is sent into rehab by Lamb. During one scene, Shirley is seen smashing a bus's windscreen with an electric iron, her anger issues on full display. To this, Lamb says:"You're going to rehab."As the teaser concludes, Shirley is seen fist-fighting with a biker equipped with a machine gun, before accepting the reason behind her admission into rehab:"I’m here to get on top of impulse control issues."All these details hint that Slow Horses Season 7 might finally adapt Shirley's story from Bad Actors. Shirley is known for her volatile temper and abrasive persona. Her character went through a rough patch after her fellow agent Marcus Longridge was killed during a shootout in the Slow Horses Season 4 finale. While Shirley had immense guilt, PTSD, and grief over Marcus' death, Seasons 5 and 6 barely touched on Shirley's trauma.It looks like Slow Horses Season 7 will finally explore Shirley's story from Bad Actors and allow her to understand her trauma and addiction by going to rehab.Slow Horses Season 7: What happens with Shirley in Bad Actors?A still from Slow Horses (Image via Instagram/@jack.lowden)While it is difficult to speculate how much of Bad Actors would be adapted in Slow Horses Season 7, it's safe to say Shirley will return to rehab.Bad Actors readers will remember how Shirley was placed in the San, a Service rehabilitation facility in Dorset, by Lamb, through Catherine Standish's intervention. Shirley's story gets chaotically intertwined with the central plot after a political advisor mistakenly believes a Russian agent is hiding under Shirley's name at the facility. The action kicks off when a group of football hooligans is sent to raid the San in search of the missing agent, which brings them face-to-face with Shirley. Shirley naturally holds her ground at the San with her fellow patients and triggers a fire alarm to fight off the intruders.While Bad Actors intertwines Shirley's healing journey with the main action, the book's conclusion offers much-needed hope for the character. Once the dust settles, Shirley accepts (probably for the first time) that she is not fine. She returns to the San after accepting she needs help.After six seasons of violence, guilt, grief, and trauma, Shirley deserves a chance at redemption in Slow Horses Season 7. If the upcoming entry remains faithful to Herron's Bad Actors, it will do justice to the character, and fans might get to see Shirley on her healing journey.In addition to Aimee-Ffion Edwards, Slow Horses Season 7 will mark the return of the main ensemble cast, namely Gary Oldman, Kristin Scott Thomas, Saskia Reeves and Christopher Chung. Jack Lowden's River's fate is unknown after the Season 6 cliffhanger. Although River survives the poisoning, his limited presence in Bad Actors hints at reduced screen time for Lowden in the upcoming season.For the latest scoops on your favorite TV shows and movies, follow SoapCentral.