Oscar Rankin is a junkie and supplied Sherlock Holmes with drugs when he was an addict. He is malevolent, clever and has never forgiven Holmes for turning away from a life of drugs.
|After Holmes is questioned as a suspect for the murder two years prior of Maria Gutierrez, he is forced to seek out his former drug supplier, Oscar. Holmes was an addict when Maria was murdered and believes that Oscar may have information on her disappearance. During lunch, Oscar lies that he doesn't remember Maria. Later, Detective Bell provides Holmes with names of regulars at a soup kitchen Maria worked at which includes Oscar. Holmes confronts Oscar who says that it was Holmes that killed her and he threatens to tell the police. Holmes believes Oscar is being truthful and later, Holmes is arrested. Watson confronts Oscar who didn't turn Holmes in and he gives Watson evidence that leads to the real murderer. Holmes offers Oscar a reservation at a rehab centre but heavily criticizes him. Oscar vows that one day Holmes will be like him. ("For All You Know")|
|To get back at Holmes, Oscar kidnaps Alfredo and demands Holmes help find his junkie sister Olivia in exchange. Oscar leads Holmes to all the sites Olivia has been to, including Hemdale and a heroin den, hoping that Holmes will relapse. When Holmes finds Olivia dead and evidence that Oscar knew she was dead before he kidnapped Alfredo, he realizes that Oscar wanted to push him over the edge. Holmes beats Oscar, fracturing his skull and ribs, and taking a heroin kit Oscar tempted him with, he relapses. ("A Controlled Descent")|
- "The whole point of this is that you remember. How you got here, who brought you."
- ―Oscar to Holmes
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