Tax evasion by fraud or suppression triggers show cause notices requiring tax, interest and equivalent penalty, with settlement windows. Determination and recovery where tax is not paid, short paid, erroneously refunded or input tax credit wrongly availed due to fraud, wilful misstatement or suppression. The proper officer serves a show cause notice requiring payment of tax, interest under section 50 and a penalty equal to the tax, with timing constraints and supplemental statement rules; voluntary payments and staged reduced penalties can conclude proceedings, the officer may issue an order after representations, and assessment orders must be issued within a specified statutory period. 'Suppression' is defined as non declaration or failure to furnish required information.