West Bengal Chief Minister Mamata Banerjee on Sunday launched her fightback with a mega rally in Kolkata-her first since Trinamool's 12 seat setback in the Lok Sabha elections. She took the bull by the horns, calling on BJP to return black money to offset BJP's cut money campaign. She also said the BJP's Bengal result was a mystery and not history and a return to ballot boxes would wipe out the party's mysterious gains.