If Tarun hosted the party to celebrate Bani's recovery and Rano's birthday, then who invited Pia and Jai, obviously not Tarun, cause Tarun asked Jai why he was there. Either Tarun is helping Jai secretly or some other person invited the guilty couple.
The other question is why has Pia turned so evil? Exactly what prompted this odd twist of behaviour for her? Does anyone know the answers?