non file return for purchase above 30 lacs

i am Mohan Bhogan in the FY 11-12 We purchased agri land in rural area for Rs 3370000/- between 3 partners, and my share was 31% only. that amount also paid by my partner's as loan to me. and same FY i haven't filed return.
now I have got notice from income tax dept. and they are asking me about return details.
in this case what to do?
regards