- The EMT says Beckett is 31 when she's brought into the hospital (technically May of S3), so she was indeed 29 at the start of the show.
- The sniper who shot Kate used a Mark 11, modified sniper rifle, which is a favorite of Special Forces. It was issued to a Navy SEAL named Martin Holst, who was killed in action, and the gun was never recovered. They did get DNA from the weapon, but it didn't match anything in the system.
- Josh did know about Johanna's murder, apparently, though presumably not all the details.
- Jim has a cabin somewhere. Beckett spent two months there, recovering, so she must have spent a month in the hospital since Gates says she's been on disability for three months. Presuming she was shot in mid-May (as the show normally runs in real time), that would mean this episode actually takes place mid-August.
- Beckett has definitely not contacted Castle for three months, and presumably not Ryan or Esposito either. However, Lanie says she hasn't talked to her in weeks, not months, so they may have been at least briefly in touch.
- The new captain is Victoria Gates, nicknamed "Iron Gates", who started her career as a detective in Internal Affairs.
- Beckett is the youngest woman in the NYPD to make detective, six weeks younger than Gates.
- Gates threw Castle out, but he uses his old friend the Mayor to get back in.
- Kate and Josh broke up sometime during her recovery.
- Montgomery sent the envelope to an old friend whose last name appears to be Smith. The same man seems to appear just behind Castle as he's primping in the mirror on his way to see Beckett. If so, he appears to be a doctor in that hospital. He tells Castle he owes Montgomery his life and apparently has enough clout with the Dragon to strike a deal to keep Beckett safe as long as she stops investigating. Whoever Smith calls after he receives the file works in the Congressional offices and he uses a special phone to do it.
- Beckett's PTSD makes a brief appearance here, but she has it under control by the end of the ep. It will reappear big time in 4x09.
- Raglan, McAllister, and Montgomery left a money trail from their kidnappings, but the bank closed. The documents moved to a warehouse in Union Square, but three weeks after Beckett's mom's murder, the warehouse burnt down. The investigator, Rod Halstead, called it an accident.
- Smith's file contains a picture of Halstead and he doesn't call Castle till after Beckett goes ballistic on the guy, so her suspicion that the investigator was paid to doctor the report may have been correct. It's likely that Halstead called either the Dragon or Smith to warn them that Beckett was sniffing around again.
- Castle is using his Smartboard as a murder board to figure out who hired the sniper that shot Beckett.
- Authors don't sign the dust jackets of books; it would rub off too easily. They usually sign the title page.
- "The killer was in the apartment the whole time" in 2x16, as well.
- Whether intentional or a goof, this is the first episode which is definitely not in real time, as Beckett's recovery period is three months, not four.
- The return address on Montgomery's envelope is 299 1st Ave, NYC, 10003. There is actually no such address, but 297 would be Gilman Hall (officially 347 E17th St), which belongs to Beth Israel Medical Center. Since Montgomery lived in a detached house with a lawn, this could not be anywhere in Manhattan. It's open to question whether the address means something to Smith, or it's just a production snafu.