Property Dispute for Flat in an Apartment building

I purchased a flat in an apartment. The builder and plot owner had development agreement of 1.5 years but builder took 3 years. While i was buying flat i did not know about development agreement. Now there is dispute between builder and plot owner and owner says he owns all building flats and builder cannot sell flats without his permission since he could not complete work in time. But i purchased flat, Registry is there and also bank gave me loan. So can the plot owner claim for all flats in Court? What is the best step possible here? Manoj