|Ua Nalohia (In Deep)|
|Season 4, Episode 7|
|Air date||November 8, 2013|
|Written by||John Dove & Noah Nelson (Story), Bradley Paul (Teleplay)|
|Directed by||Joe Dante|
While working the murder case of an undercover ATF agent, McGarrett and the Five-0 team must solve the case with help from Captain Lou Grover. As this happens, Mary returns to the island with a newly adopted baby daughter, with Steve and the team being forced to babysit Mary's baby daughter after Mary is hospitalized while suffering from salmonella.
Five-0 investigate the murder of Bryan Carpenter, but later learn he is Matt Hutchins, who Chin recognizes as a former police academy cadet. He was working deep undercover for the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) to infiltrate a gang of gun runners lead by Jason Dekker. After finding $100,000 cash belonging to Hutchins, Danno suspects he turned bad.
However, it is later revealed that Dekker loaned him the money, and Hutchins was using it to find a mole in the ATF, who is feeding information on rival gangs. The leak is revealed to be Linda Davies, Hutchins's handler's assistant, whose boyfriend killed him when he was too close to identifying the mole.
Meanwhile, during the course of the investigation, Mary returns with her adoptive baby daughter, who the team have to look after while Mary has food poisoning.
Catherine captures Kuroda and later learns of Sato's location, after which she officially joins Five-0.
- Joan McGarrett, Mary's adopted baby daughter, is introduced for the first time.
- Charlie Fong officially returns to the team, having recovered after being stabbed weeks ago.
- Catherine officially joins the H50 team.
- Chin Ho Kelly: to Steve "Why is there a baby attached to your chest?"
- Danny Williams: "Uh, Mary."
- Chin Ho Kelly: "Ah. Say no more. Mazel Tov."
- Steve McGarrett: (Steve walks into the HQ with Mary's baby attached to his chest)
- Danny Williams: (laughs hysterically)
- Steve McGarrett: (smiling) Is this funny to you?
- Danny Williams: (laughing) Yeah!
- Steve McGarrett: So when you're through amusing yourself, I need you to wipe down her changing pad please.
- Danny Williams: No, no, no, I'm retired, you see. And it's going to be way too entertaining to see Uncle Steve on diaper duty so go ahead.
- Grace Park is credited, but do not appear.
- When Steve, Danny, and Chin take care of the baby. Their actions are reminiscent of the film, Three Men and a Baby (1987).
|Alex O'Loughlin||A Navy SEAL and leader of the Hawaii Five-0 Task Force.|
|Scott Caan||2nd-in-command of the Hawaii Five-0 Task Force and Steve's partner.|
Chin Ho Kelly
|Daniel Dae Kim||A member of the Hawaii Five-0 Task Force.|
|Grace Park||Youngest member of the Hawaii Five-0 Task Force, and cousin of Chin.|
|Dr. Max Bergman||Masi Oka||Chief Medical Examiner for the Hawaii Five-0 team.|
|Catherine Rollins||Michelle Borth||An Ex-Navy Lieutenant and Steve's on-off girlfriend.|
|Lou Grover||Chi McBride||Captain of the HPD SWAT team.|
|Dr. Charles Fong||Brian Yang||Forensic Scientist who works for the HPD and H50.|
|Mary McGarrett||Taryn Manning||Steve McGarrett's little sister.|
|Hideaki Kuroda||Brian Tee||A Yazuka boss.|
|Cheri Tranton||Daryl Hannah||A woman who appears in the episode.|
|Jason Decker||Xzibit||The leader of a group of local gunrunners.|
|Agent Blake Kennedy||French||An agent with the ATF.|
|Allison Hutchins||Floriana Lima||A woman who appears in the episode.|
|Linda Davies||Christie Burson||A woman who appears in the episode.|
|Matt Hutchins||Westley LeClay||The murder victim.|
|Ray Ballard||Finn Armstrong||A man who appears in the episode.|
|Nani||Cathy Foy||A woman who appears in the episode.|