Petty Officer Collins death was ruled an accident, but Laura was suspicious.
She got sick before she could investigate further, and now shes running out of time.
Quinn attributes it to the two of them being naturally gifted runners.

Credit: Cliff Lipson/CBS
But okay, down to business.
The U.S.S.Graywas patrolling South American waters on a counter-narcotics mission when Collins disappeared.
Not, like, Abby goth, but dark lipstick, nose ring, no-eye-contact goth.
Baxter tattles that Collins and Laura were in a relationship, which was against Navy rules.
Curse your smug untouchability, Baxter!
Someone was trying to hide something.
Something like… murder?
twirls mustache
Okay, sorry, very little about this episode is funny.
The women ignore his twitchiness, and Laura tells Bishop that she and Collins werent in an inappropriate relationship.
Says the guy who had four dead bodies in his apartment, Quinn says.
Five, McGee corrects her.
Hey, at least he owns it.
Alas, they find Trainer in her apartment, dead from a heroin overdose.
Torres isnothappy about this and demands, Why me?
Gibbs says they both need to do their jobs.
She finally calls him on it, saying shes learned to read people since her diagnosis.
Some are sympathetic; others pity her.
She says she understands and is sorry for his loss.
But Torres isnt interested in Hallmark moments and shuts that down.
Baxter insists he had nothing to do with Collins death and is shocked to learn that Trainers dead.
He says he didnt tell NCIS because he didnt want Trainer to get in trouble.
She found out that morning, he says, as they watch her laugh and chat with a doctor.
If the weather wants to kill me, itll have to take a number, she jokes.
He drapes his coat over her lap and stands stiffly next to her.
Laura, ever the chatterbox, apologizes for speaking too bluntly to him.
At first Torres is silent, and then he tells her, I dont like clutter in my workspace.
Deep, she says drily.
But hes making a point.
Laura knows the end of this story and asks, When was she diagnosed?
It was their senior year, and both of them believed the treatments would work… until they didnt.
She accepts because shes an exceptionally well-written guest character.
When Gibbs tells Laura that theyre arrested Vinton, she frets that she shouldve done more for Collins.
He had a good role model, Gibbs tells her.
Because you did, Nick.
And then they settle in for some ZNN.