Determination of Fraudulent Tax Evasion: notice triggers liability for unpaid tax, interest and escalating penalties; prompt payment concludes proceedings. Determination of tax liability arising from fraud, wilful misstatement or suppression is initiated by a show cause notice requiring payment of specified tax, interest under section 50 and a penalty equal to the tax; the officer must issue the notice at least six months before the limitation for assessment, may serve a supplemental statement treated as a notice under section 73 where grounds match, and must determine and order tax, interest and penalty within five years from the return due date or erroneous refund.