The memory of Marco Reyes will not let Danny sleep easy on Hawaii Five-0.

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Danno(Scott Caan) may not show it, but the death of his brother and his own revenge on the killer continues to haunt him. A new sneak peek for this Friday's "Nahanhu (Embers)" dips into the detective's private life, showing that Danny is having nightmares about Reyes (see video below).

Unable to sleep, Caan's character spends part of the night walking around, eventually passing out on a hammock.

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Five-0's most cantankerous member may soon have new fuel for his nighttime musings. Episode 18, "Pono Kaulike (Justice for All)," will see both Danny and Chin pay for their involvement in Reyes' death. Danny for the criminal's murder, and Chin for the money he borrowed from his former brother-in-law.

"There's going to be a price to pay for what [Danny] did," executive producer Peter Lenkov told TV Guide. "The same with Chin Ho borrowing the money from Gabriel - that's going to come to a head also."

Find out more when Hawaii Five-0 airs Fridays at 9 p.m. ET on CBS.