“Os” is episode sixteen of season three of Fringe.
Walter is smoking a bong with a security guard, Kevin, at Massive Dynamic, watching the monitors when he asks what the room is no-one goes in. William Bell’s office.
Walter turns up at Nina Sharp’s office with a trolley of boxes containing Bell’s old research files. Walter has to protect their world and he’s feeling he’s let people down. For the first time since they reunited, Peter is happy – Nina didn’t know Peter and Olivia are a couple – but Walter is missing his old friend and is wondering how to succeed without him. Walter remembers how good they were together, and if he goes through Bell’s old files, he might remember to think the way they used to.
Two men are climbing up the side of the Massachusetts Metal Depository. One reaches the top. Where a pair of boots are hanging upside down. He puts them on and starts walking off upside down. A security vehicle arrives as the second is trying to put his boots on. Except it turns out they were straining to climb down the side of the building, not up. The second gets shot by a guard and bobs into the air, stopped from floating off by the rope.
Peter is working in the Harvard Engineering Building on the memory discs he retrieved from the shapeshifters it turned out he was hunting in “Reciprocity”. He’s found some previously undetected data but has no idea how to read it. Olivia rings to invite him to a street fair. Peter says he’s not at home, he’s at the gym and will meet her.
After the call, Olivia gets a text message from Broyles wanting her and the Bishops. They arrive at the Metal Depository as the body is being pulled down. Walter is excited. They have a sketch of the second man and the guard says they’ve been through the precious metals and nothing is missing. Broyles is given a key card taken from the dead man, which isn’t used at the depository. Then an agent says they know what the thieves took.
Peter has found the spare pair of boots; they’re waited. He and Walter look at the body, which has atrophied calf muscles. Which would happen if someone floats, except his chest and arms are normal and they should be wasted too. Olivia joins and asks what they know about osmium; chemical symbol ‘Os’. Lots of it are missing. Peter says it’s rare but not that valuable and Walter mentions it’s twice as dense as lead. Like using balloons to steal bowling balls.
Two people are leaving the Frost Aerodynamics building. The second robber is there, waiting for one, Dr Krick. He explains the other is dead. He’s also nauseous and his head is killing him. It didn’t feel like this last time, but he has what Krick wanted. Krick tells the man to wait for Krick at the lab.
Peter is looking through William Bell’s files looking for stuff to do with floating. The dead man seems to have a weakened immune system and the effects are wearing off. Olivia arrives. The key card has been traced to a warehouse and she and Peter leave.
Krick arrives at the warehouse to find the thief there, bleeding from his eyes. Krick says you can’t defy gravity without consequences. He’s telling the man he’s a pioneer, helping Krick to eliminate the side-effects, and Krick believes they’re almost there. The man, however, is dead.
The other robber falls out of the air at Walter’s lab. He asks Astrid to put the body on the table. She can’t; he’s too heavy. Walter tries too. The man is far heavier than he should be. He wants the man’s blood tested for osmium. Astrid asks how osmium could make someone float. It can’t. That’s what troubles Walter.
Krick has severed the dead man’s foot and is taking samples when he sees Walter and Olivia being let in on a monitor. He’s gone by the time they get there. They find the dead man’s body. And, it turns out, a whole lot more.
Walter arrives and says they all had toxic levels of osmium in their blood. Injected. Walter doesn’t know how injecting the world’s heaviest element would make people float. Broyles has found eight wheelchairs. And they have IDs on a few of the bodies. They all suffered from muscular dystrophy. Walter realises that is what caused the muscle wasting and wonders why he missed it.
Injecting people with something heavy is making them float. This concerns Walter a lot. He doesn’t think he can manage without William Bell, and wants to get him back.