The story could end with the book's reception after all 25 installments are released, any follow-up actions, and how it's received in academic and political circles. Perhaps some historians start using it as a source, while others criticize it as self-serving.

In terms of structure, a detailed story could be broken into sections: Introduction to Mengistu, the context of his exile, the significance of the book's title, the format (25 installments), the content overview, public and governmental responses, analysis of the content's credibility, and the legacy of the book in Ethiopian history.

I should also consider any possible collaborations or individuals involved in the book's production. Maybe exiled Ethiopian writers, translators, or publishers in countries where he's granted asylum. The process of writing, editing, formatting as a PDF, and distributing it.

Now, the book "Tiglachin" is his new work. The name "Tiglachin" sounds like it might be Amharic or another Ethiopian language. I should verify the possible meaning. Maybe it's a symbolic term or refers to a specific period. Since the book is released in 25 installments, it could mean it's a serial publication, each installment covering a chapter or a theme. The PDF format suggests it's accessible online, maybe through the internet or some digital platform, especially since Mengistu might be in exile and can't distribute books in Ethiopia legally.