In Cordoba, Argentina. Mac and Jack are trapped in a trash compactor and the walls close in. Hack checks with Wilt and Riley, who are outside the bad guys' compound. Riley tells them that the mercenaries don't know where they are so the compactor must be on a timer. She can't hack the controls, and Jack tells Wilt to stand down rather than move in and get shot. Mac warns Jack that the pipe he wants to use as a strut can't take the pressure, but sticks his knife in the pipe end tries to get to the hose with the hydraulic fluid. He punctures the hose and stops down the compactor, while Riley sets off an explosion as a distraction so that they can escape even though Jack breaks his arm.
Later, back at Phoenix, Matty tells Mac that Jack is in the infirmary with a fracture. Mac admits that that he was too focused on stopping the motor and used a technical term that Jack couldn't understand. Matty points out that Jack was the one who got them into the compactor in the first place, and asks if Mac needs a partner who can speak his language. Before Mac can respond, he gets a call from a friend, Frankie, and abruptly walks out to take it. Wilt says that Frankie is a close friend of Mac's from MIT and goes after his friend. Out in the hallway, Mac takes the call and says that he'll be there. The others come out and he tells them that there was an accident and Frankie is dead. Matty gives him time off to go to a memorial in Boston.
Mac arrives at the Boston terminal and finds a limo waiting for him... with Jack dressed as a driver. He says that Wilt called him and told him what happened, and they drive off.
Wilt approaches Riley and suggests that she give him a tutorial. She's busy on her phone texting to Kalei, and agrees to tutor Wilt later. Once she leaves, Matty figures that Wilt still has a thing for Riley. She warns him that there's nothing there and it's time for him to move on. Wilt tells her to mind her own business, and Matty says that it's on her time and it is her business.
Jack drives Mac to the memorial and offers his condolences on Frankie's death. Mac says that there was a fire in her lab, and that Frankie was way out of his league smarts-wise. Jack doesn't believe it, and Mac says that she was an expert in DNA and one of a kind. He talks about how Frankie could have changed the world.
At the memorial, Richard Sang gives the memorial speech and says that he was privileged to be her principal sponsor. Mac makes a Moebius strip out of a piece of paper and tells Jack that Frankie used to love them. Afterward, Devon "Smitty" Smith comes over and thanks Mac for coming. They hug and Smitty mentions that Dr. V died. He explains that the doctor's car went off the road in a snowstorm, and he went into a coma and never came out.
Jack comes over and points out someone taking photos, and Mac approaches the man. The guy walks off and Jack grabs him. The photographer hits Jack in the arm and runs off, dropping his phone. Mac goes after the man and Jack follows. However, the man disappears and Jack checks the phone. There are photos of everyone at the service, and Mac wonders why Frankie's faculty advisor died in a car crash a month before she died. He finds photos of Frankie's burned-down lab on the phone.
At the lab, Jack discovers that the fire supposedly started at an electrical box. Frankie's remains were found five feet from the south wall and the fire consumed her body. Mac says that it isn't what happened and says that it was a bomb, and finds a spectrometer at the heart of the explosion... with a detonator in it. They realize that it was no accident.
Mac and Jack call in and Matty points out that he's taking an unsanctioned leave. They admit that Jack's arm isn't better and Mac explains that Frankie's death was no accident. Riley traces the cell phone and discovers that he was sending an email with the photos but it didn't go through. Matty tells Mac that she needs him back in 48 days for an assignment.
Once they sign off from Frankie's garage workshop, Jack suggests that they consider the human angle: what was the motive. Mac points out that the fire started in the lab, and she was working on a new DNA sequencing technique. The technique could put a lot of medical research companies out of business. The lock on the door is new and there's a new surveillance camera pointing toward the street. Mac notes hat Frankie never left anything online, and spots a flowerbed nearby. He explains that they physically backed up their information and finds a flash drive buried beneath the plants. It's her journal, and in the last entry, Frankie says that she thinks someone tried to break into her lab. Frankie tells whoever is watching that if something happened to her then it wasn't an accident.
Riley calls and tells them that she traced the last physical location of the email address. It's on campus in The Tombs, a cluster of old buildings that no one uses. The two men go there and Jack stops a booby trap on a door. Mac cuts the tripwire and discovers that it's rigged to a cell phone to let someone know that a person opened the door. jack points out that detonator was also makeshift and it all looks like Mac's work. They see a figure in a hoodie run by and go after the person. Mac splits away to take a shortcut, and tackles the figure. He yanks off the hood and discovers that it's Frankie.
Frankie takes Jack and Mac to the quarters that she's rigged up. She admits that she faked her death and Jack explains how they found her. Frankie thought that whoever wanted her dead would show up at her funeral. She's surprised that Richard gave her eulogy, and doesn't see any strangers. Frankie explains that her thesis let her recover full genomes from derided DNA. They asked the police for blood samples from closed cases, and they were able to reconstruct any of them. The Boston PD sent them a cold case and her lab blew up just as she was going to ID the killer. Frankie went to her lab and stumbled over the detonator, so faked her death rather than risk another attempt.
Jack suggests that the killer has the police on his payroll, and Frankie shows them the blood sample. She wonders how they can analyze it, and they call Phoenix. Riley pulls the police file on the case, which involved victim Ronald Manning, a reporter shot to death in his backyard. Frankie says that a lot of people knew she was working with the Boston PD, and Mac suggests that they use Frankie's process to identify the killer.
The trio breaks into a campus lab after hours, and Mac and Frankie conduct the process to separate out the DNA. Jack goes to check the perimeter and Frankie admits that it's crazy to be working with Mac again. She points out that he left without explanation.
Wilt calls Jack and asks him for advice about dealing with Riley. He says that he's stuck in the friend zone, and Jack tells him that it's always up to the girl. As Jack tells Wilt to start taking no for an answer, he sees two black SUVs pull up. Jack goes back and tells Mac and Frankie that they have six men coming in. Mac insists that they have to go rather than let Frankie die again. They're forced to hide in a storage room, and Jack prepares to take on the men. Mac says that he has an idea and creates an electrical whip out of electrical cords. They go back out to the hallway and take out the men, and Frankie wonders what Mac has been doing since he dropped out of school.
Back at Frankie's quarters, Mac tells her what he's been doing. She's surprised that he's now a spy. Riley calls and tells him to take all of the wireless chips out of Frankie's laptop. Frankie does so and Riley explains that someone planted spyware on Frankie's laptop and that's how they found her. She's unable to trace it back to the killer, and Frankie figures the men will go after her parents if they can't find her. Mac says that he can't let her walk away from her work, and tells her that if she runs then she's dead. Frankie insists that they can't recreate the sample without a lab, and Mac says that they'll need to make a lab.
The next day, Jack goes around campus gathering equipment, claiming that they're making moonshine. As Mac cuts properly proportioned disks out a box, Frankie asks why he left and became a spy. He says that his grandfather called when one of his war buddies died. It made Mac realize that while he was trying to solve theoretical problems, soldiers were dealing with real problems. He dropped out and enlisted, and ended up defusing IEDs in Afghanistan. Mac then reveals that he made a centrifuge out of cardboard and shoelaces, and it will separate her blood sample.
Once they resequence the DNA, Riley is unable to find a match. Mac and Frankie figure that they can' sketch the killer from the data, and Wilt says that he can do better than that. In Once he has the info, he creates a head sculpture from the data. Wilt shows it to others, and they realize that it's Richard: one of the most powerful men in Boston.
Richard is dedicating a new building while the trio watches from a nearby car. Riley sends information confirming that Manning was going to expose Richard for massive fraud. Frankie says that if they can get a DNA sample of Richard then she can prove she's the killer. However, her technique only works on blood.
After Richard dedicates the building, Frankie approaches him and asks if they'll continue financing DNA sequencing. Mac tries to get to Richard and his security guards lead him off. Jack punches him, getting Richard's blood on his ring, and asks the campus security guards arresting him for an evidence bag. Once Riley gets the sample, she confirms a match with the killer and Richard is taken into custody. Mac calls to thank them, and Matty tells them to get back home. Jack hugs Frankie and leaves her with Mac. Frankie asks if she could convince Mac to stay, and he says that he has work but suggests that she call him if she just wants to talk.
As Wilt and Riley pack up, Kalei calls. She hesitates and Wilt apologizes for not taking her hints seriously and making things weird about her and Kalei. He tells her that he's ready to be her friend, and they go to get burgers.
As they head to the airport, Jack tells Mac that maybe he should stay there. He admits that he's feeling like the dumb one and Mac belongs with his own kind. Mac says that he doesn't want to work at a MIT lab and he does want to work with Jack.
Written by Gadfly on Apr 1, 2017