Hawaii Five-0's Shelburne mystery has been simmering for four years, but the case may reach a boil in season 5.

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Every time Steve McGarrett appears to unravel the secrets surrounding Doris McGarrett (Christine Lahti) and Wo Fat (Mark Dacascos), another one seems to pop up to take its place. However, Jerry Ortega (Jorge Garcia) and his obsession with conspiracy led McGarrett to finally understand the connection between his mother and the master criminal.

Now that Wo Fat is back on the island and looking for a meeting, McGarrett may have a chance to find out where Wo Fat's father really is since he definitely isn't in his Cambodian grave. Unfortunately, that information may be slow in coming.

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"In the world of "Five-0," the Shelburne story arc is always going forward, especially now that we have both Doris and Wo Fat in the wind," explained executive producer Peter Lenkov, according to the Honolulu Pulse. "We just may not see where it's going quite yet. But we will..."

Find out more when Hawaii Five-0 returns to CBS on Sept. 26 at 9 p.m. ET. Click the video below to see a preview from the series' latest episode.

Tags: Hawaii Five-O CBS television