Warning! SPOILERS about Outlander season 7, episode 5, and the Outlander books ahead.
Brianna's interview for her new job was already challenging because of her employer's expectations, but Outlander season 7, episode 5 even proved her subordinates happily gave her a hard time because she was a female plant inspector. Rob Cameron and Andy Pfeiffer locking her in one tunnel at Loch Errochty scared Brianna, but proved also particularly enraging because she could feel it was more than just hazing, as there had already been remarks about her being a "madam inspector." While she easily got out of the unfortunate situation because she knew the schematics, the ordeal still put Brianna on a collision course with Rob Cameron, whom the others seemingly looked up to.
The seventh book on which Outlander season 7 is based, An Echo in the Bone, cements Brianna's coworker Rob Cameron as her antagonist. Cameron's welcome at work already unnerved Brianna, but the seventh Outlander book also had him sneak around Lallybroch, leading him to learn about Outlander season 7's Jacobite gold and time travel. Cameron's vast knowledge of Loch Errochty's tunnels, coupled with his kidnapping of Jeremy in An Echo in the Bone, rightfully worried the Mackenzies already. However, Brianna's discovery of the tunnel portal in Outlander season 7, episode 5 also speeds up a big worry for the Mackenzies that eventually brings time travel back into their lives.
Rob Cameron's discovery in Outlander's seventh book An Echo in the Bone that Jemmy Mackenzie supposedly knew the location of the Jacobite gold based on Jamie and Claire's letters gave him the idea to kidnap Jemmy, using him as a way to get Roger and Brianna to convince him to tell him the location. Brianna and Roger knew about Jemmy's knowledge of the location without being privy to it hiding the lost Jacobite gold, but they also refused to ask about it in Outlander season 7, episode 3. This made Jemmy unaware of how important the secret location he shared with Jamie could have been to others.
Cameron tricked Brianna and Roger into letting him leave with Jemmy with the excuse that he organized a playdate between his nephew and Jemmy in An Echo in the Bone, but his intent was always to bring Jemmy to Craigh na Dun. Only when that didn't work Cameron hid Jemmy in the tunnels, but that still scared Brianna, as she knew the Loch Errochty tunnels hid a time-traveling portal. Outlander season 7, episode 5 set up Brianna's knowledge of that portal, hinting at the TV show soon tackling this book story, especially as the episode also set up the acrimony between Brianna and Rob.
Believing that Rob Cameron succeeded in bringing Jemmy back in time in a bid to find the Jacobite gold, Roger and Brianna decide to follow both probable outcomes by separating. If Cameron hid Jemmy in their timeline, Brianna would have worked to find him in the 1980s, but if Cameron brought Jemmy back in time, Roger leaving for the past with his ancestor Buck would have found them. Outlander season 7, episode 5 continued building up on Jemmy's talks about Nuckelavees, turning the tale into something more sinister, as even Roger saw food wrappers, while Mandy saw someone around their premises, which scared her.
With Outlander season 7, episode 5 cementing both the antagonism between Brianna and Cameron and the bigger presence of Buck Mackenzie at Lallybroch, it's indubitably setting up time travel returning to the Mackenzies' lives. Indeed, Buck provided help to Roger by accompanying him to the past to find Jemmy in the Outlander seventh book, and while that didn't work because Cameron never succeeded in bringing Jemmy to the past, it still causes Bree and Roger's separation, along with a return to the 18th century. In advancing this story, Outlander season 7, episode 5 brings Roger and Bree one step closer to the rest of their family in America.