McGarrett (Alex O'Loughlin) has "a LOT" of questions for his mentor, CBS teased. That's certainly understandable, as Joe was last seen in the Season 2 finale, when he introduced McGarrett to the mysterious "Shelburne," aka McGarrett's mother.
O'Quinn most recently starred on ABC's short-lived drama 666 Park Avenue.
Are you looking forward to seeing O'Quinn back on Hawaii?
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