In case you skip it...

Dr. Zimmerman, the creator of the Emergency Medical Hologram and the closest thing The Doctor has to a father, is dying from a mysterious untreatable illness. Barclay advises The Doctor of this via one of Starfleet’s monthly data streams, and The Doctor thinks that he can adapt Borg regeneration techniques to save Zimmerman - but no doctor in the Alpha Quadrant is familiar enough with them to treat Zimmerman.

Thus, The Doctor convinces Janeway to send a compressed version of his program as Voyager’s response for the month, putting off their own letters back. The Doctor thereby visits Jupiter Station to treat Zimmerman himself, leaving Paris in charge of Sickbay for the month Voyager will have to wait before Starfleet can send him back.

The Doctor does manage to successfully treat Zimmerman and returns to Voyager after another month, but the episode unfortunately isn’t particularly enjoyable. Still, it’s good to know that this happened.

It’s also revealed in this episode that back in the Alpha Quadrant, the EMH Mark I (the line to which The Doctor belongs) has been retired in favor of more advanced models. The existing Mark I holograms were apparently retooled to perform menial labor such as scrubbing plasma conduits on waste transfer barges, to Zimmerman’s great embarrassment.