Gibbs (MARK HARMON), Tony (MICHAEL WEATHERLY) and Kate (SASHA ALEXANDER) are called to a gruesome scene. During a training exercise, Marine Corporal Larry Fuentes has plummeted to his death -- straight through the roof of a parked SUV -- when his parachute didn’t deploy. As the trio interrogates his fellow corporals, Ducky (DAVID McCALLUM) examines the corpse, and Abby (PAULEY PERRETTE) begins running forensic tests on all the parachutes and other materials gathered at the scene. The interrogations with Fuentes’ fellow unit members -- Dafelmair, Brinkman and Ramsey -- yield little at first, except that Fuentes was nicknamed “Thumper,” because he was the luckiest guy to have around: always walking away unharmed from disastrous accidents and raking it in at the poker table.
With Abby finding signs of battery acid being spilled on Fuentes’ parachute lines, Gibbs and Tony take a look at the paraloft where the chutes and reserves are locked and stowed. The investigation quickly points to the chutes’ rigger, Lance Corporal Billy Webb who, Gibb discovers, has had a previous record for robberies, and actually even served jail time. His record has even spawned a nickname that often provoked threats from him toward his Marine cohorts. Still, Abby’s preliminary findings uncover that the logs to check the parachute equipment seem to have forged signatures for Webb, and that there are two sets of fingerprints on the deployment bags’ knots. With that, Gibb tries to tap into the Armed Forces’ DNA Registry to identify the names behind the prints. While Lt. Bud Roberts (guest star PATRICK LABYORTEAUX) knows that database can’t be accessed for suspect information, he does agree to help Gibb with search warrants for several corporals’ lockers in the paraloft.
During that search, the case becomes more complicated as an exacto knife is found in rigger Lance Corporal Schilz’s locker. But when Kate and Gibb question him, a shell- shocked Schilz unflinchingly agrees to a DNA test. With Abby backlogged, Gibbs assigns Kate to help her, and the two quickly forge a friendship while performing more forensics testing. They determine that Fuentes’ suspension lines were cut, possibly with the exacto knife that’s been found. Then, when keys to the paraloft are.
found in Webb’s footlocker, Gibbs’ suspicions are focused on him again. During Webb’s questioning, he vehemently claims innocence, but lets Gibbs know he doesn’t believe Schilz is guilty either. Abby’s further findings vindicate Webb; his fingerprints don’t match those found on the rigging. However, there are Schilz’s and another unidentified set.
Armed with this information and losing out on Webb as prime suspect, Gibbs thinks somebody targeted Fuentes, trying to hide a murder behind sabotage. He focuses on Fuentes’ behavior once again, and wonders about all his previous, “lucky” accidents. Delving into them, the agents find a series of recent accidents that plagued Fuentes, but all miraculously left him unscathed. And upon remembering the corporals’ reference his luck at the poker table, they find that Fuentes’ checking account has been routinely pumped up with frequent cash infusions. The agents then begin to piece together that those poker games may have left one of the other corporals in serious debt, and – to avoid it -- he could have resorted to murder, rigging a parachute to end both Fuentes’ life and money troubles.
With Fuentes lucky streak in mind, Gibbs deduces that drawing “13” to parachute in – while deemed unlucky for many – wouldn’t have mattered to Fuentes. And that was indeed the number on his reserve chute. So, with the tampered chute, Gibbs and Tony take to a C-130 with all the suspected corporals for a mission. There, high in the sky, Gibbs asks Dafelmair if he wouldn’t mind taking chute 13. Although Dafelmair doesn’t seem to mind at first, his confidence soon crumples and – not eager to skydive to his death – he admits to killing Fuentes. In his confession, he identifies angry accomplice Ramsey, who was also eager to get out of debt and conspired with him.
And all through the case, Gibbs tries desperately to avoid the continual bleat of his cell phone, with ex-wife number three eager to reunite on the other end.