S1·E4 The Mata Hari Affair

Someone is after belly dancer Mata Hurens, who has a message for Mr. Waverly. She boards a train for London as does April who is trying to see to her safe arrival. However, a bomb has been planted on the tracks. The train derails and many are killed, including Mata Hurens. April survives and is determined to find the murderer. By impersonating the dead bellydancer, April hopes the killer, thinking he's failed will make another attempt. Then, April and Mark can capture him.