The Aventures of Tintin in the Congo is a bit different fromother Tintin books. Basically Tintin is on vacation in Africa to shoot animals with gun and camera. Camera only comes into play in the last eight pages of the book when he has already shot 15 antelope, a monkey, a large snake (which was eating a man, so not really bad to kill) and an elephant. Probably people are going to do racism to death in the other reviews. I don't see it as much of an issue. Most scenes show Tintin alone in the forest shooting animals, so there are no natives to portray negatively. (If British people were in the mood to complain about Thomson and Thompson they could.) Obviously the racism issue is why this Tintin book gets released less frequently than others.
The plot as previously stated has Tintin on a big game hunting vacation in the Congo. On the boat ride over Snowy gets into scrapes with a parrot, an electric fish and a stowaway who remains undiscovered except by Snowy. In the Congo the stowaway follows them and keeps trying to cause trouble for Tintin. Is he still mad about Snowy or does he have deeper motives? ....
Read some other Tintin books before you read this one. TIntin does do clever things for example using an electro magnet to escape danger and assuming a disguise to unmask a crime ring. However he also does clever things like feed alkaseltzer and water to a big cat and get a snake to start swallowing its own tale. Mostly he is just shooting animals and getting rescued by Snowy or missionaries and is basically passive.