Alfredo and Sherlock watch Abbott and Costello on the roof. Alfredo is hoping for a text or call from a former flame who moved away. Alfredo leaves early because he has a job tomorrow.
Sherlock still doesn't have a sponsor. He is meeting a promising candidate tomorrow at Alfredo's garage. When he arrives, Alfredo is missing. Sherlock finds Alfredo's phone smashed on the ground.
Joan joins Sherlock at Alfredo's garage. Sherlock is worried that he has relapsed.
Sherlock's former drug dealer, Oscar, needs help finding his missing sister, Olivia. He claims to have taken Alfredo and will release him after Sherlock finds Olivia.
Captain Gregson and Bell are upset that Sherlock went with Oscar instead of contacting them. Sherlock isn't worried about Oscar and wants them to look for Alfredo.
Oscar's sister is an addict who recently went to rehab. She called Oscar a couple days ago to tell him she was leaving. He admits he kidnapped Alfredo because he didn't think Sherlock would help him otherwise.
They go to Hemdale Rehabilitation Center to talk to Olivia's roommate. She says Olivia was going to meet with Beta Ray. Oscar knows where to find him.
Joan and Bell search Oscar's place. They see Alfredo's Charger is parked outside and find evidence that he was in the trunk. Joan spots a greasy Dilby's napkin under the seat.
Oscar takes Sherlock to a heroin den.
Olivia and Beta Ray are supposed to come back tonight. Oscar says they need to wait.
Sherlock calls Watson. He tells her about dust he found on Oscar's coat. She wants Sherlock to leave.
Sherlock wakes up Oscar. He found a license belonging to Jonathan Bloom. Sherlock is worried that Olivia left with him.
They go to Bloom's home. There are rumors he preys on young woman who are hooked on drugs. Sherlock hits him. He claims Olivia robbed him and left in a cab.
Bell wants to apply more pressure on Oscar's uncle.
Oscar and Sherlock go to where Olivia had been dropped off. Sherlock goes into a tunnel and finds Olivia.
Olivia has been dead for two days. Sherlock found Oscar's boot prints next to her body. Sherlock wants to know why he lied.
Olivia called Oscar after she left Bloom's place. When Oscar found her, all of he could think about was Sherlock. He wanted to see Sherlock fall.
He tosses Sherlock some drugs.
Joan and Bell find Alfredo. He is alive but dehydrated.
Joan texts Sherlock with the news. Sherlock punches and kicks Oscar. He picks up the drugs and walks into the tunnel.
Joan tells Sherlock that his father is coming.