For many, July 4 weekend invokes images of picnics and fireworks. However, for Lesa Buchanan and her boyfriend Christ Koulis, it was a weekend of sex and drugs that eventually resulted in Buchanan’s death. Buchanan was struggling to make it as an actress and model when she had a chance meeting with Koulis, a handsome, ambitious plastic surgeon. She became his patient and his girlfriend. Although the couple maintained a five and-a-half-year relationship, according to Buchanan’s family it was marred by Koulis’ manipulative and controlling behavior. They say that as a doctor, Koulis would convince Buchanan she was ill so he could make her better. Koulis admits he introduced her to illegal drug use, which authorities say the couple engaged in to enhance their sexual encounters. According to a police investigator, the only time Buchanan experienced those drugs was when Koulis gave them to her. On the weekend of July 4, 2005, paramedics were called to Buchanan’s Franklin, Tenn., apartment because she had stopped breathing. Police would later discover a cache of sex toys and prescription drugs. An autopsy concluded that Buchanan died of a narcotic overdose. Authorities launched a five-month investigation, eventually charging Koulis with her death. Despite Koulis’ denials, detectives say that his grip on Buchanan led to her drug use - that he supplied the drugs, injected them and was responsible for her death. Prosecutors were convinced they had a strong case. Koulis, a once-promising young doctor, finds himself standing trial and facing 25 years in prison for the death of his one-time patient and girlfriend, and Buchanan’s family hopes that justice is served in the name of their loved one. 48 Hours correspondent Troy Roberts reports on the case this Saturday, Feb. 16, at 10 p.m. ET/PT.