Got summons from lower court

i got a summons for a property which i a had agreement(non registered) to sell in dec 2013 to party2.the party 2 didnt register the land n i sent notice in 2015 to him.property is in karnataka. summons mension i am needed to solve issue related to my property due to dispute between party 2 & party 3 for which i was not a witness n not aware of ,how to proceed sir