WARNING: Spoilers for The Haunting of Bly Manor ahead
After it’s revealed that Peter Quint (Oliver Jackson-Cohen), Henry Wingrave's (Henry Thomas) valet, is strangled to death by The Lady of the Lake in The Haunting of Bly Manor episode 5, “The Altar of the Dead”, Peter as a ghost always wants Rebecca Jessel (Tahirah Sharif) - the previous governess at Bly Manor - to meet him in the forbidden wing, but why does he pick that particular location? Since Peter is able to appear at will anywhere on the property as a ghost, one theory suggests that Peter picked the master bedroom within the forbidden wing as he and Rebecca’s secret meeting place for a more nefarious reason.
While The Haunting of Bly Manor begins by following the perspective of the new governess Dani Clayton (Victoria Pedretti) as she cares for the orphaned children Miles (Benjamin Evan Ainsworth) and Flora Wingrave (Amelia Bea Smith), it eventually shifts to show the afterlife of the ghosts at Bly Manor. In Mike Flanagan’s modern television adaptation of Henry James’ novel The Turn of the Screw, the main ghost that haunts Bly Manor is memory for both the living and the dead, specifically their past trauma, unfulfilled dreams, and failed relationships. One of those memories is the ghost of Peter and Rebecca's relationship, which became toxic due to Peter’s controlling and possessive nature that persists into his afterlife. While Peter eventually possesses Rebecca and drowns her in the lake to trap her spirit at Bly Manor with him in the episode “The Two Faces, Part Two”, it’s possible that Peter initially had another plan to get Rebecca killed by the Lady in the Lake.
In episode 8, “The Romance of Certain Old Clothes”, the Lady in the Lake is revealed to be Viola Willoughby (Kate Siegel), a former resident of Bly Manor who experiences an untimely death at the hands of her sister, Perdita (Katie Parker), after being sick with “the lung” for years. Haunting a chest filled with expensive clothing that is eventually discarded into the lake instead of passed down to her daughter, Viola walks the same pathway every night, out of the lake and up to the master bedroom in the forbidden wing and back, mimicking insomniac behavior she exhibited while alive. Since Peter was one of Viola’s victims, Peter knows firsthand that it’s possible to be killed by accidentally crossing Viola's path. With this in mind, Peter's perfectly reasonable request for Rebecca to meet him in the forbidden wing at night is transformed into a sinister murder plot, especially since he refused to tell her how he died.
Further proof that Peter might’ve been planning for Rebecca to be killed by the Lady in the Lake can be found when analyzing Peter’s knowledge of his afterlife at Bly Manor. By the time that Peter and Rebecca have their rendezvous in the forbidden wing, Peter already knows that he’s trapped at Bly Manor. When Rebecca suggests that they go to America as they had planned before Peter’s death, Peter says that he’s tried to leave the premises, but he can’t get passed the gate, which is later revealed to be due to Viola’s gravity well. Given Peter’s possessive nature, the only other option that would allow him to keep Rebecca at Bly Manor would be to get her killed, with the way he died being the most convenient option. After Rebecca never coincidentally bumped into the Lady of the Lake’s pathway, however, Peter then resorted to his backup plan to spiritually possess Rebecca and kill her himself.
Whether or not this theory is correct in The Haunting of Bly Manor, one could also argue that Peter and Rebecca were often present in the forbidden wing because it's symbolic of their unfinished business. The master bedroom is filled with valuables that formerly belonged to the wealthy blue blood owners of Bly Manor, Charlotte (Alex Essoe) and Dominic Wingrave (Matthew Holness). The opposite of the Wingraves, Peter and Rebecca wanted to attain the wealth and status they weren’t born into, Rebecca by becoming a barrister and Peter by stealing money from his boss. Since Peter and Rebecca died before either of them could accomplish their goals, much of the wealth present in the forbidden wing will always be within reach, but will remain “forbidden" to them.