Investigating an explosion, the team finds traces of acetone peroxide, typical of Middle Eastern terrorists, suggesting a terrorist cell in Hawaii, traced to a terrorist hideout to prepare an attack at a military base where the Secretary of Defense is speaking at an event, where the thug commits suicide by cop. Five-0 and HPD secure the area, locate and disarm the bomb, but the terrorist responsible has escaped. can't move or it explodes. As the bomb squad works to defuse the device, Steve distracts Danny from his anxiety by making him tell how he escaped death in New Jersey. Danny recalls the incident in 2001, before '9-11', when he and then NYPD partner Grace Tilwell were captured and tortured by drug gang members Ray and Billy. The gang members kill his partner before Danny could escape and kill all three members responsible. At the time Danny's wife was pregnant; it's implied that he named their daughter Grace after Tilwell.
—KGF Vissers