This is a book about a salvage operation on a very unusual planet.
Mesklin is a disc-shaped world, the disk bulging out at the poles, rather like ()
But also there's a strong gravity differential between the rim and the poles.
At the world's edge the gravity is about 3 times that of Earth's- tough going but manageable to the human crew. But at the poles it is many hundreds times that of Earth, crushing to any human, literally.
The native inhabitants are rather like large centipedes, with flattened bodies and multiple limbs-this helps them to cope with the strong gravity at the poles. These inhabitants are traders, and sail across their world in a ship called the Bree, trading goods with whatever races they happen across.
At some point there was a mission from Earth, and one of the crew's rockets, containing expensive cargo and equipment, worth billions, crash landed at one of the poles. Of course the humans are unable to go to the site as they would be crushed, and so they enlist the aliens they find there, whose bodies are designed to withstand the high gravity.
When the book opens the human crew have been at Mesklin for quite some time already and the language barrier has been crossed; the two races communicating via 'vision sets' provided by the humans. The Mesklinites continue with their trading operations, while also helping the humans to find their abandoned ship. The aliens, being so small, have a very low view of the world and have a strong sense of fear of things being above them. Quite understandable really because when at the poles a fall of a few inches could be catastrophic, and anything with any mass falling on them would be fatal. As such their homes have cloth roofs, and they have no concept of flying or even throwing.
The book is definitely hard SF, written by as scientist who makes the reader understand that throwing an object on a world of super high G, let alone flying, would be inconceivable. On such a world a bullet from a gun would arch down to the ground shortly after being fired, and at such a high G place even a pebble, if dropped, would create a huge crater. As such there is no war,no weapons. Also the 'geography' of the planet is quite different. The seas are composed of methane, not water. This is far less dense than water and so the aliens are able to float their ships and travel. For me it made fascinating reading and considering this was written in the 1950s it is quite cutting edge with its strong hard SF elements and, apart from the often wooden dialogue, it appears timeless.
On the whole
I found this to be a well laid out exploration of a truly alien world with an interesting collaboration between the humans and the planet's native race and how the barriers are broken down between them.