Crystalline Green
performed by Goldfrapp

House is confronted by Kalvin, a flamboyant homosexual man who demands treatment when other doctors diagnose him with AIDS, something he admits he does have. House begins making moves on Stacy using sensitive information on her relationship with Mark.

t is John and Mary's wedding day and Sherlock is daunted by the task of delivering a Best Man's speech. As part of the speech, he recounts cases they have worked on including a soldier being stalked and somehow stabbed in a locked shower, a ghost dating women he dubs "The Mayfly Man", the last being part of John's disastrous stag night, among others. Before his speech ends, he realises that a murderer is present among the guests intent on killing a fellow guest. Sherlock informs John and Mary of the meaning of the sign of three. The title is based on the Holmes novel The Sign of the Four.