This is generally regarded as the first "proper" Tintin book, and I had of course read it ages ago. I now realise that it shares a lot of the flaws of the generally disregarded first three, Tintin in the Land of the Soviets, Tintin in the Congo and Tintin in America; there are brutal racial stereotypes, most of the story being set in Arabia and India, with the odd token African; the plot, such as it is, revolves around a rather ludicrous criminal conspiracy with a tendency to hide in well-lit and well-ventilated underground lairs (just like the Soviets did in the earlier book); and there's a rather disturbing obsession with mental illness as comic relief. One interesting point is that the villains are involved in illegal drug trafficking, specifically cocaine with hints of heroin, a theme Agatha Christie also used in Evil Under the Sun a few years later. Another is the self-reference - an Arab chieftain greets Tintin by showing him a copy of Tintin in the Congo which he has acquired (more recent editions paste in instead the cover of Destination Moon, which actually comes later in the sequence). Basically not really as good as I had remembered, alas.