This is the worst of the Silver Brumby books - even Silver Brumby, Silver Dingo is a little better - and is a real slog. I read somewhere that Mitchell felt pressured to write this story because her fans were horrified that she had killed Thowra off at the end of the previous book, and it shows.
This story follows Yuri and her foal by Thowra, Wirramirra, a silver colt. Yuri is just as flat and bland as a character as in the previous book, somehow made worse because now she is a mother and yet remains incredibly unintelligent. Kulali has to save her from herself multiple times and she nearly gets Wirramirra killed at the start of the book, before actually getting Kulali killed later. She insists on travelling to Thowra's country to find him, yet the journey that took only a few days in the previous book seems to take an excruciatingly long time in this one.
The book takes on a bizarre taste of the supernatural, with the constant references to Wirramirra basically being Thowra reborn, and the white hawk being heavily implied to be Thowra shapeshifted. Additionally, Wirramirra is constantly referred to basically as if he was Thowra's only silver son, when Lightning and Baringa exist.
But worst of all is the timeline holes the story creates. Before this story, it was easy enough to imagine that the events of Whirlwind took place some years after the events of Kingdom. However, partway through this story, Yuri, Wirramirra and Karee meet Kalina. Now, apart from the pure ick that Yuri openly settles for Kalina because she can't have Thowra and Kalina looks rather like him, Kalina is given a definite age.
Kalina, who was born at the end of Kingdom and is Baringa and Dawn's son, is described as being four years old. By the time Yuri and Wirramirra meet Kalina, it has been two years since the end of Whirlwind, which means Kalina was a two year old during the events of Whirlwind. Which means that Thowra, Boon Boon, Golden and Storm have gone from being sprightly and alive during Kingdom, to aged and dead, in just two years.
An additional hole in the story is that Kalina takes everyone to the Tin Mines at one point, and even into Dale's Creek - and yet there is no mention of his own sire, or that he might take Yuri and Wirramirra to the Canyon, which would be a perfectly logical place to take them.
It also means that the eclipse in Moon Filly happened during the events of South, which the characters in South DEFINITELY would have noticed, and that the fire in South happened during the events of Moon Filly, which again, should have been noticed. While I appreciate that Mitchell was trying to tie the characters together, the choice of Kalina, and the age given to him, immediately blows several large plot holes in her timeline, which really affects the enjoyment of the story.