Sherlock and Alfredo are watching Abbott and Costello on the roof. Alfredo leaves early because he has a client meeting tomorrow. Sherlock still does not have a sponsor but Alfredo is going to introduce him to a promising candidate at the garage. When Sherlock arrives, he finds Alfredo's smashed phone. Sherlock's former drug dealer, Oscar, calls him for help. Sherlock is unwilling to help until Oscar mentions Alfredo. If Sherlock will help find Oscar's missing sister, Olivia, then he will release Alfredo. Captain Gregson and Detective Bell are unhappy when Joan tells them Sherlock left with Oscar. He claims he can handle Oscar but wants them to continue their search for Alfredo. Olivia recently went into rehab but called Oscar to let him know that she was leaving. Sherlock and Oscar talk to her former roommate who says Olivia was meeting someone called Beta Ray. Oscar takes Sherlock to a heroin den to find them and does drugs while they wait. Meanwhile, Joan and Marcus search Oscar's place and discover Alfredo's car parked outside, but no Alfredo. Where has Oscar stashed Alfredo? Will Sherlock be able to resist temptation with all the drugs readily available? Watch Elementary Season 3 Episode 24 online to find out the answers.