First appearance of John Nolan's ex-wife Sarah, played by Emily Deschanel. The character previously made a cameo as a voice on the phone in season one, played by a different actress (Season one, episode eight: "Time of Death," after Nolan fatally shoots his first suspect).
Both Emily Deschanel (John's ex-wife Sarah) and Nathan Fillion (John) formerly played in serial crime dramas as novelists who end up helping law enforcement based on their knowledge base and also got married to members of law enforcement that they worked closely with as consultants (Fillion as Richard Castle, a writer shadowing the police for research, in Castle (2009); Deschanel as Dr. Temperance "Bones" Brennan, a forensic anthropologist who wrote crime novels on the side and examined murder victims for clues, in Bones (2005)).
This episode is what is known as a "bottle episode," an episode set entirely (or nearly entirely) in one location. This is typically done because of restrictions like finances, but in this case may have been done in part because of the restrictions of filming during the COVID-19 pandemic (which, given the cost increase to productions that precautions required, may also mean increased financial restrictions). Characters being in hospital beds or required to stand on opposite sides of hospital beds from each other also helps to make the six-foot minimum distance between them seem natural.
Tony Amendola (Tomás Madrigal) is another Once Upon a Time alum, alongside Mekia Cox (Harper) and previous recurring guest stars Karen David (a detective throughout season two and early season three here, who notably had a problem with Lopez dating a defense attorney, and Princess Jasmine on Once) and Jeff Pierre (Lucy's firefighter boyfriend earlier this season here, Prince Naveen on Once). Amendola played the recurring character of Gepetto/Marco throughout the entirety of the series while Cox played first recurring and then main character Princess Tiana/Sabine in the seventh (final) season (Pierre played her love interest).
The building used for the hospital in this episode (at least the exterior shots) is next door to the building that has previously been used as the exterior of the Mid-Wilshire Division, most easily seen in the episode where Nolan is held hostage outside (episode 3x5, "Lockdown"). The same building has previously been used by other crime dramas, including NUMB3RS and 24.