Shaw competes his trilogy which began with 'The Ragged Astronauts' and continued with 'The Wooden Spaceships'. The reader does really need to have read those books first. The premise is that twin planets, Land and Overland, are close enough that an envelope of atmosphere allows one to travel between them by hot-air balloon. Yes! Go read the first ones! They are great!
This tale is set many years on and the grandson of Toller from those books is having a busy life. He falls for a higher-status young woman, he is contacted by aliens and he gets to go on an interplanetary voyage to Farland, a third planet in the system. As the people do not have much metal they are still making wooden spaceships and have developed a propulsion system based on maths - burn for long enough then stop, open the door and look out to see if you are there. Hmmm.
The tale is not so convincing and while there are many links with the earlier books, it is definitely the weakest of the three in various ways. Read the first two, which stand alone, and then read this at your leisure just for the sake of completion.
A different work by Shaw and my favourite, is 'Other Days, Other Eyes' which tells of his marvellous invention slow glass.