Notice u/s 148

my client is govt employee and he recieved a notice u/s. 148 for reasseesment for asstt year 2009-10 he already filed the return in specified time period but there is mistake in return.he havent shown capital gain in his return. he sold his house in 2009-10 in 1500000/- which he has purchased in 2004-05 in rs.390000/- and further he renewate the house also and invest arround rs. 450000/- but he dont have bills for this amount. total indexed cost comes to arround rs. 1100000/- he invested 865000/- to purchase a land but the problem is that land was commercial. now what we have to do please tell in briefly we have to file new return or what will be the reply.