An unseen person assembles a sniper rifle.

Elsewhere, Jane makes Maura go for a run as she heals from donating her kidney to the sister she didn't know she had. She insists she's OK with her decision, but Jane says the sister is being ungrateful.

At the St. Patrick's Day parade, Frankie shows his mom the motorcycle he just bought. Angela tells Maura she's worried about her. Frankie announces he's getting promoted to detective. Maura offers to help him fix his bike.

Senator Malcolm Humphrey and his daughter Erica go by in a convertible in the parade. She won his seat in the state senate.

The sniper takes aim from a window above and shoots Erica Humphrey in the head. Frankie and Jane spring into action and go up to the room where the shot came from. The victim's sister shows up at the scene with Erica's young child in a carrier. Jane doesn't think they're looking for a pro, the shooter threw up after firing.

Later, in the morgue, Maura is still bummed she hasn't gotten a thank you from her mother for donating her kidney, even though she told her mom not to contact her.

The victim, Erica Humphrey, has a five day old wound on her shoulder that could be from barbed wire.

Upstairs, they review the victim. Her sister, Jennifer, who showed up just after she was shot at the parade, was her chief of staff.

Maura comes up to report the bullet fragmented so she can't trace it.

Maura asks to talk to Jane. She finally admits to herself that she's bummed about not hearing from her mom and she wants to know if her sister Cailin is taking care of her kidney.

Suzy the lab tech comes up to report finding blueberries in the victim's stomach, matching the blueberry waffles in the shooter's vomit. They had breakfast together.

They wonder if her husband Jeff Miller could have killed her. He got mocked as a house husband when she won.

Lt. Cavanaugh asks Jane how Angela is doing and says to give her his best.

At Erica's office, Jeff addresses Erica's staff. Jane and Frost think he sounds like he's running for office. He thinks his wife was killed because she was backing environmental legislation. He shows them a threat she received.

Jeff and Jennifer don't know about Erica's breakfast meeting. Her calendar says "THT." Tomorrow's entry says "Deliver GBS." Jeff was at their kid's soccer game when his wife was shot. He refuses to give a cheek swab.

Frost finds four bottles of dirty water in bottles under the sister's desk.

Maura meets Jane and they spy on Cailin getting coffee; she sees them. Jane forces Maura to go talk to her.

Cailin apologizes to Maura for how she treated her and thanks her for the kidney -- she guessed it was from her. She gives Maura a package and asks if she can text her some time.

Maura opens the package, it's a scrimshaw (whale bone) necklace that her mob father Paddy Doyle gave to her mother, Hope.

Back at the office, Frost and Jane look into a website, Stop Bad People. Korsak reports the bullet was a .22. Jane finds Maura hanging upside-down on a gravity inverter in her office. She's worried about her father's impending murder trial.

In interrogation, Korsak, Frost and Jane talk to Ishmael, the young, nervous, nerdy man who runs the website. He says he was hired to harass Erica Miller online, but he doesn't know by whom.

Later, Frost says soccer parents only remember seeing Jeff Miller at the beginning and end of the game. Jane sets Frankie on figuring out where Erica had breakfast.

Maura reports the dirty water was well water mixed with soil. Her hard drive had test results from soil in Reedville.

Jane and Maura run to Jane's place to check on her dog and she finds Casey on her doorstep. He's walking again with braces. He was misdiagnosed originally and they opened him up and found shrapnel pressing against his spine. Maura runs off, leaving Casey to walk Jane's dog with her.

Casey tells her PTSD kept him from contacting her sooner. He kisses her and they head back to her place and get in bed. He stops, telling her he wants them to be in love before they go any further.

In the morning, Casey tells Jane he's going back to Afghanistan for a few months to give training in virtual therapy for combat soldiers. He wants to try again with her when he gets back.

In the office, Maura talks Jane out of looking for reasons to be scared about getting involved with Casey.

Maura gets results that there was dirt from Reedville in Erica's wound.

Jane checks in with Frankie, who gives her the name of a diner in Reedville that serves blueberry pancakes. Jane drags Maura with her to check it out. The waitress tells them something is poisoning the children in town.

The Honeysuckle Battery company is in town. Maura found Hairy Honeysuckle pollen in Erica's wound; it lines the factory barbed wire fence. They think she snuck in. Maura says battery toxins could be carried home as "Take Home Toxins" by the workers -- or THT like Erica wrote in her calendar.

The owner of the company, Bill Davenport, was out of town when she was killed.

Erica wrote a grant that gave $2 million to Honeysuckle Battery for environmental safeguards. They think the company misused the funds. They notice who was in charge of compliance.

Later, they meet with Jennifer, Jeff and Malcolm Humphrey. Frost tells Jennifer he traced payment to the harassing website back to Jennifer.

Flash back to Jennifer taking aim at her sister as the baby hangs out in a baby carrier.

Three months ago, Erica started testing the water and soil in Reedville but she found nothing. So she traced it to the new Honeysuckle Battery company. They think Jennifer took a bribe to cover it up. "Deliver GBS" stood for Good-bye Speech. Erica was going to resign and take responsibility for what Jennifer had done.

Later, at Maura's house, Jane and Frankie tinker with his motorcycle. Angela comes home with Lt. Cavanaugh. The head into her place to make dinner together, and other things Frankie and Jane try to block out.