Mirrorpix/Mirrorpix/Getty ImagesWhen Doctor Who returned to TV screens after a long absence — a decade or a decade and a half, depending on how you count the 1996 TV movie — the 2005 relaunch seemed to simplify the canon for a new generation. The titular time-traveling Doctor was now the last of the Time Lords, and a vague, complex event in his past might have rewritten some of the pre-established timeline. And while “Season 1” of the relaunched Who made several references to the classic 1963-1989 series, one question remained: Did the Time Wars of the past rewrite the Doctor’s continuity on Earth? Today, there are still some wibbly-wobbly questions about contemporary canon relative to the machinations of the Toymaker in 2023, but in 2006, with one Season 2 episode, Doctor Who seemed to make one thing very clear: The past happened, and the previous, classic companions of the Doctor were still around.On April 29, 2006, Doctor Who, Season 2, Episode 3, “School Reunion” found the Doctor (David Tennant) and Rose (Billie Piper) embarking on a good-old-fashioned-aliens-hiding-in-a-school plot. Featuring Anthony Head of Buffy fame as the evil Mr. Finch, “School Reunion,” at least at a glance, has the plot of one of the more forgettable early Tennant adventures; its monster and concept are no more memorable than “The Idiot’s Lantern” and its production values, today, somehow look more dated than the 1970s and 1980s versions of the show. But nobody loves “School Reunion” for the monster-y sci-fi plot. The reason why “School Reunion” is immortal and a great Who episode is that it featured the return of Elisabeth Sladen as Sarah Jane Smith, the previous companion of both the 3rd (Jon Pertwee) and 4th (Tom Baker) Doctors. Like the Doctor and Rose, Sarah Jane is investigating the fishy school for signs of otherworldly activity, which echoes her original role as an investigative journalist in the serial “The Time Warrior.” The brilliance of bringing back Sarah Jane to the Who mythos is that this episode is twofold: First, it firmly establishes that contemporary Doctor Who is meant to be seen as the same continuity as the classic series, and that the Doctor carries all the memories from all their previous incarnations, including the groovy 1970s. But, more tenderly and intelligently, the episode also paints the Doctor in a new light, at least for viewers who were getting used to a young, flirty version of the character. The 10th Doctor may look and act youthful and cartoonish, but he’s very, very old, and the proof is right here: a middle-aged woman who was once a young woman who, like Rose, travelled with the Doctor and endured a regeneration, too.At the time, Sladen was 60 when “School Reunion” aired, which is interesting, considering that David Tennant is 55 now, in 2026. To put it another way, she wasn’t that old in “School Reunion,” but considering the characters of Rose Tyler and Mickey Smith (Noel Clarke) were meant to be 19 and roughly 24, Sarah Jane was witnessing the notion that she had been replaced by people who were about her age when she first started traveling with the Doctor. In a fantastic scene between Sarah Jane and Rose, the two women initially spar over their shared experiences, but then find a common bond. In real life, the audience realizes that the Doctor constantly ditching his companions for younger people would be creepy as hell, but what Sladen and Piper remind us in this scene is that we’re all in love with the Doctor, too, so that’s why we give them a pass.Elisabeth Sladen in | Mirrorpix/Mirrorpix/Getty ImagesSladen’s return as Sarah Jane Smith to the modern Who mythos wasn’t just limited to this episode, of course. She would return again in the fourth season, massive two-parter, “The Stolen Earth,” and “Journey’s End,” as well as her own spinoff series, The Sarah Jane Adventures (which is sort of like the Whoinverse version of a live-action Star Trek: Lower Decks, but also kinda YA). Broadly, Sladen’s return as Sarah Jane grounded modern Who in its nostalgic roots, but also elevated the pathos of the series. Sladen’s acting chops in “School Reunion” bring Tennant and Piper to a new level of reality, which sounds strange considering the goofiness of Who, but is undeniable upon a rewatch of this episode. What could have been a forgettable episode about brain-sucking aliens is instead a story about heartbreak, aging, and finding meaning with ones life, even if some incredible part of that life is over. Sarah Jane tells us that it’s okay to move on without giving up, which, in sci-fi and fantasy narratives populated by mostly young people (or older people who look young), is surprisingly powerful. Sladen’s subsequent appearances in the Whoniverse following “School Reunion” prior to her passing in 2011 are all wonderful. But of all her performances, even in the 3rd and 4th Doctor eras, “School Reunion” is probably the best. Like the Doctor, Sarah Jane gets to exist in the past and the present at the same time, and in terms of stories not about the Doctor, Doctor Who has rarely been this profound or sweet.Doctor Who (2005-2022) is not currently streaming on any major service. However, you can rent episodes on Apple TV, Prime Video, and elsewhere. Classic episodes of Who, featuring Sarah Jane Smith, starting with Season 11 (1973/1974) are streaming on Tubi, Pluto TV, and BritBox.