Gibbs, Robert M. - G.R.I.
The Postage Stamps of the German Colonies occupied by the British 1914-1918Publisher: Christie's - Robson Lowe, London, 1988.
Hardback, dustwrapper, illustrated, xv + 275 pages, very short tear to dustwrapper, few tiny dusty marks to upper page-edges, ex libris National Philatelic Society with small library stamp to verso of title-page, internally clean, in Good condition.
The definitive handbook on these issues. Very detailed, and well illustrated. Out of print and hard to find.