Agent Farnsworth uses her clearance to cross the bridge to This Side, then goes off the grid. Bolivia thinks she can find her.
At Harvard, Peter's annoyed when Walter wants yet another food break while working on the Machine. Walter misses the other boy, the one who plays chess and doesn't starve him. Sorry, Lincoln's off celebrating his goddaughter's birthday.
Farnsworth walks in and says hello. With her uniform, red-highlighted hair, and rapid-fire, flat speech, she's obviously not their Astrid. Soon, she's telling Astrid that they lowered the box into the ground, and they put down flowers, and she didn't know where to go afterward. Tearful, she asks: Yours, did you love him?
Olivia asks what's going on. Astrid says I think my - her - father is dead.
The Fringe team has a case, but Olivia's double is coming to get Farnsworth. Outraged, Walter thunders, Olivia, the viper?! Olivia wonders if someone should stay there, but Walter says, Astrid and I can wait here alone. Astrid's bugged that Walter got HER name right.
The team tracks a killer who carries a glowing blue rod and claims that he's sparing his victims a life of agony. Both have bloody tears on their faces, reminding Walter of the mythical Tears of Ra, a painless, instantaneous poison Egyptians supposedly used to euthanize beloved pets. At the first crime scene, an Observer watches the team, then reports over his phone that he thinks he has located it.
Walter isolates the poison. The compounds in it shouldn't interact, but they do. It's not magic, it's . . . unusual science. Bolivia arrives, much to Walter's displeasure.
Suddenly, Farnsworth says, "Deus ex machina." She explains that someone would have to see the chemicals being combined in order to know how to combine them, and the chances of that occurring randomly are incredibly small. Therefore, a root of the equation is outside their realm of causality. The hand of God - or godlike forces, says Walter, impressed. He thinks he loves her!
Walter gives an amused Bolivia some "junk" she left. He thinks one mysterious item, a small metal cube, is another tool of her spy-craft. She teases that he should just admit he likes her.
Farnsworth observes that Walter is angry with his son. He denies Peter's his son and says looking at Peter is painful. She says that if he chose to believe Peter was his son, then he could love him and be happy. Walter considers this.
The killer, Neil, is a TSA screener at Logan International Airport. As the same Observer watches, he tries to "save" another victim, Jared, from his tragic life after a car accident. But Jared runs . . . and gets hit by a car. Now a paraplegic, Jared tells Olivia and Peter that the man wanted to put him out of his misery, like it was a good deed.
Walter refuses to give Bolivia any Red Vines. Farnsworth finds a connection: All three victims were cleared by the same TSA agent at Logan. Walter says, I told you: I love her!
Neil gives Peter and Olivia the slip at the airport. At MIT, where Neil was a math professor, they learn that Neil found something mysterious at his lake house a couple years ago. He became obsessed with these high-level differential equations, believing that solving them would let him see past, present, and future simultaneously. Where was this house? Reiden Lake.
Peter tells Olivia that seeing across time is what the Observers do. And in his own timeline, one saved his life at Reiden Lake. At Neil's lake house, they discover his father and twin brother died in a car accident.
Walter sits under headphones, thinking. Astrid makes Farnsworth her first cup of coffee; it's very rare on the Other Side. Farnsworth asks if Astrid cares for Walter, like a father? Haltingly, she confesses she's afraid she couldn't give her father a deeper relationship, like he wanted, because of . . . the way she is. Tearful, she asks if he could've loved her more if she were like Astrid - normal? Astrid looks thoughtfully at Walter.
Neil locks the rod in a safe and loads a gun, then confronts his confused mother. When his brother, Alex, died, he heard her say God took the wrong one. But now God's given Neil a way to see the future, so he can bring people mercy. When Olivia and Peter arrive, he reminds his mother what the priest said about Alex: Angels don't belong on Earth. I'll see you in heaven, he says, then turns and fires. Olivia kills him. Now Neil gets to be an angel too.
Before heading home, Bolivia shows Walter that her mysterious "spy tech" actually holds a tasty snack. Walter gives her a Red Vine, and maybe he likes her after all.
Astrid tells Farnsworth that she and her father aren't very close, either. He's a complex man and doesn't really show emotion. He does the best with the tools he has, and she knows he loves her - at least, she tells herself that. She says don't regret that you could've been more for him. It wasn't you.
At home, Astrid's father is making dinner. He gives his baby girl a big ol' hug, and they say they love each other. So who was Astrid talking about?
December and the other Observer retrieve the rod from Neil's safe. It's September's - he must have lost it in 1985, the night he didn't save the boy. The other Observer informs December that September apparently did not obey instructions. "The boy is back."