Hint: Largest after the "Big 4"
Answer: Grant Thornton International
Grant Thornton International is a global organisation of accounting and consulting member firms which provide assurance, tax and specialist advisory services (SAS) to privately held businesses, public interest entities, and public sector entities. Grant Thornton International Ltd is a not-for-profit, non-practising, international umbrella membership entity organised as a private company limited by guarantee. Grant Thornton is incorporated in London, United Kingdom, and has no share capital.