Snowstorms in a hot climate : a novel / Sarah Dunant.

Enhanced descriptions from Syndetics:

Marla's best friend, Elly, left England two years ago on a soul-searching trip through South America. Except for receiving a few postcards, Marla has not heard from her since. Then, Marla receives a strange letter from Elly begging her to fly to New York. But the person Marla meets at the airport is a very different woman from the strong, carefree friend she remembers. Elly, now well-dressed and thin, has acquired a park-view apartment, a house in the Hamptons, and a charismatic, manipulative, cocaine-smuggling boyfriend named Lenny.

As Marla tries to free her friend from the dual addictions of love and cocaine, she unravels a story of seduction and power in Columbia and of desire and betrayal in California. Caught in a web of deceptions, the threat of violence mounting around them, Marla decides to take on Lenny and his empire. But Lenny-like the drug he peddles-has no intention of letting Elly go.