Watson comes home to find Sherlock boxing up her things to move to the brownstone.
A woman sells jewelry for cash. She approaches a homeless man and gives him a bag of food. She shoots him and leaves an envelope of cash with a note on his body.
The amount of money left on the victim connects to Arlen Schrader, a victim's compensation attorney. He became famous for his formula on the value of a person's life.
He points them to his ex-girlfriend. She said he broke-up with her because of a case involving Aceway Flight 1059.
At a support group meeting, the killer watches a man speak. Afterwards, they have sex. She sees him smoking and notes it changes the amount. She shoots him and adjusts the amount of cash in his envelope, which she leaves on his body.
The killer is targeting beneficiaries of the victims of the Aceway Flight 1059 crash. The Aceway CEO admits that they are considering another formula where they pay a fixed sum, which benefits more of the victims.
The killer's sister tells Dana that the bank is foreclosing on her house. Dana says she's going to make a bigger fuss.
Joan finds out during her apartment walk-through that the new tenant requested a better deadbolt. She asks Sherlock if he wants her at the brownstone.
Gregson calls. The killer made another attempt but failed. The victim is Dana, the real killer.
Dana walks Sherlock and Watson through the attack. Sherlock asks if the man has a limp, which she didn't notice.
Sherlock wonders why a man with a physical disability would climb over fence when there were easier ways to access the property. Or attempted to shoot from a distance when all the other murder victims were shot in close range.
Dana goes to press and rails against the fixed sum payment plan, saying her husband is worth more and deserves more.
Aceway settles on the fixed payment plan. Sherlock suspects Dana but cannot reconcile why she forced Aceway to choose a formula where she would get paid less.
Sherlock admits that he rented Joan's apartment because he worried she was being too hasty and may regret her decision later. He fears that what she sees as progression, may actually be regression and he doesn't want to enable her.
They receive a sketch of the gun buyer who is Nick Powell, Dana's husband.
Dana comes home after a big shopping spree. Her sister is inside upset and suspects Dana. The police interrupt their conversation.
Sherlock and Watson tell Dana that they know her husband had an aggressive brain tumor. He was planning to commit physician-assisted suicide. If the airline used Schrader's formula, they would have uncovered her husband's illness, which would have significantly reduced her payout.
Joan takes Sherlock downstairs to see her new office. She wants to still have her own space. Sherlock tells her that he has to cancel the lease on her old apartment.