This was Kekoa Kekumano's first appearance as recurring character Nahele Huikala, the at risk youth that McGarrett takes under his wing.
Title translates 'Not Forgotten'
Grover refers to an anti-psychotic drug at one point as Chlorprozamin, this drug is in fact, Chlorpromazine. His description of what it's used to treat is correct but just his pronunciation that's off.
Another Baldwin brother appears in this episode. This time it Daniel Baldwin.
Gregory itzin and Daniel dae Kim both worked on 24