Requiem for a Killer (2011)

Lucretia is a killer for hire. Specialised in poisoning and passionate about opera, she'll have to fulfill a difficult contract in the heart of the Swiss alps. Posing as a singer, Lucretia will have to appear on the scene of the higly exclusive Festival d'Ermeux and try to kill one of her partners: British bariton Alexander Child. Having recently acquired a Scottish distillery, he remains the only obstacle to a strategic pipeline project with considerable economic stakes; having recently won a tough legal battle against British Oil, their last resort is to eliminate him. Complicating everything is Rico, sent by the French contra-espionage, who tries to infiltrate the orchestra and stop the plot against Alexander Child.

Source: TMDb