'Abdu'l-Baha - by Hand of the Cause, H.M. Balyuzi

From the Foreword section:

The first chapter of this book was written as long ago as 1939. The book owes its inception to a gracious remark by Shoghi Effendi, the Guardian of the Baha'i Faith. When my booklet on the life of Baha’u’llah was issued by the Publishing Trust of the Baha’is of the British Isles in June 1938, and copies were sent to him, he expressed his hope in a letter to the National Spiritual Assembly that companion volumes would be written on the life of the Bab and the life of 'Abdu'l-Baha. I set about organizing an outline for a book on the life of 'Abdu'l-Baha, which, because of the abundance of available material, would necessarily be of vaster proportions than the slim booklet on the life of Baha’u’llah. That booklet was reprinted in The Baha’i World, Vol. VIII (1938-40). In future years with added material it grew into a small book and came from the press in the Centenary year of the Declaration of Baha'u'llah.