The story of three people is woven together - The man who assassinated Leon Trotsky (and loved dogs), Leon Trotsky himself, and a Cuban erstwhile author. The main theme, as I read the book, is disillusion with communism, which in different forms affect all three protagonists - they have all been fervent revolutionaries and are all - in this tale even Trotsky - disappointed and disillusioned.
The book is at its best very good - which is why I kept reading even through the long middle, which was, at times, slow going - for me, the book did stagnate a bit during the passages with Mercader and Trotsky in Mexico. But all in all, it was worth the effort.
(I must say, though, I was sometimes in doubt about this translation. The language didn't always flow too well, and some word choices seemed unnatural.)