A seemingly random murder outside of UHOP sets the stage for the arrival of someone from Watson and Sherlock Holmes' past.

As Adam's wife goes in for a C-section to deliver triplets, chaos ensues when their OB-GYN passes out in the operating room. Meanwhile, a severe storm detours Watson and Mary's trip to find a renowned doctor to remove Watson's brain tumor.

Following his brain tumor diagnosis, Watson goes on medical leave to seek treatment, leaving Mary in charge of The Holmes Clinic as a notorious South American dictator demands Watson see to his mysterious autoimmune condition personally. Meanwhile, Ingrid grows more concerned about Beck's obsession with Sasha.

After a key player disappears, the team rushes to find them before it's too late.

Watson investigates a case involving a mentally unstable mother, with the woman's delusions serving as a mirror to his own newly discovered hallucinations.

Watson and the fellows race to save the life of a young woman who needs a lifesaving kidney donation. Meanwhile, Sherlock returns to help crack unsolved cases in Pittsburgh.

Watson is sued for Wrongful Life by a long-term patient suffering from VACTERL association, after undergoing multiple painful surgeries.

Watson and the fellows fight to revive a 30-year-old woman, Audrey, after her heart inexplicably stops repeatedly until they discover she has a rare phenomenon called Lazarus syndrome. As these revivals continue, she uses the short window of time available to right her greatest wrong.

When a patient arrives at the Holmes Clinic plagued by a mysterious neurological disorder, Watson and the fellows discover they were forced to eat their parents amid a childhood survival incident. Meanwhile, Adam is struggling with how his future will change as a father.

Watson and the fellows race against the clock to save a man and his pregnant wife from a terrifying sinkhole. Meanwhile, Ingrid's future with her therapy group becomes unclear.

Watson's biohacker friend Hobie (aka the man with the glowing chest) returns when he rushes his new girlfriend to the Holmes Clinic after they partake in a gene-editing experiment that goes wrong. Meanwhile, Watson becomes suspicious of Sherlock.

Watson and the fellows help Laila's son Micah, who was injured in a car accident while pursuing his crush, Bex, with the help of his AI chatbot.

Watson and the fellows are taken hostage by a man with a bomb strapped to his chest who is desperate to find a cure for his 9-year-old daughter's illness.

Watson's father, Hamish, visits UHOP to introduce Watson and the fellows to his protégé, Annabelle, a saxophone prodigy with musically induced blackouts.

Watson and the fellows race against time to save the life of Xavier, a 21-year-old athlete with a fast-growing, seemingly incurable cancer; Mycroft Holmes lets Watson know his team's work at UHOP may no longer have funding available.

While visiting another hospital, Watson becomes convinced that a man is suffering from locked-in syndrome and has been mistaken for a coma patient for over a decade; Sherlock is back in town and is staying with Watson.

Watson and the team jump into action when four people become infected with a flesh-eating bacterium; Shinwell searches for meaning as a nursing student; Adam's wedding to Lauren risks being halted.

Watson and the team work alongside Laila to help a patient named Maxine, a 30-year-old who looks 10.

When a microbiology university researcher returns from an expedition to Siberia, she and her team members fall ill from a possible revived pathogen; Watson catches up with his friend Sherlock Holmes after finding out he is alive.

Watson and the fellows spring back into action when Mary's mother accidentally poisons herself while suffering from a rare form of dementia that is progressing with impossible speed; Sherlock Holmes resurfaces after being presumed dead.