Prior enquiry and show-cause notice requirement before issuing a reassessment notice, with limited exceptions. The Assessing Officer must, with prior approval of the specified authority, conduct any necessary enquiry where information suggests escaped income, serve a show-cause notice affording the assessee an opportunity to be heard and consider any reply, and then decide whether to issue a notice under section 148 by passing an order with prior approval of the specified authority within a prescribed post-reply period; exceptions apply for cases arising from searches or requisitions or where seized or requisitioned items in another's case are shown to relate to the assessee.