The main character is Dan who used to work as a spy. He has worked with Heid, Nina and Cas and their boss was Sir Geroge. Their aim was kill the dicdaters who opposite the president.
Oneday, when Dan is sitting in a river side, someone has shot to try to kill him. Dan fall down in the river and hide from the shooter. When he looks at the shooter, he recognizes that the shooter is his former colleague, Heid. He has no idea why Heid has tried to kill him because they has been told that thye can never meet each other again when they quit their jobs. Dan gets angry with Heid because he has tried to kill him although they have been friends. He hit Heid and killed.
Dan have decided to find out the background of the event. He contacts with his another former collegue Bert who he can believe. Finally he finds out that it connects with a company which he used to work in. When he was working in the company, he saw somebody was talkin with his boss. He didn't want to be in trouble so he pretended not to notice. Of course he didn't know who was talking with his boss in that day, but he has noticed because of the event.
He gets angry with his former boss and decides to give away the secret.
At last, he has got success but also lost lots of things.
人の関係はわかりますが,Dan has decided .. 以降をそれまでと同じくらいの分量で書かないと,肝心なことがわかりません.つまり,
the secret とは? success とは? lots of things とは?
ということです.
英語の細かいミスがいくつかあります.2つだけ(目立つものを)挙げると,
someone has shot to try to kill him は語順が不自然で,また現在完了になる理由もありません.
→ someone tried to shoot him to death
fall down in the river → fell in the river かと思います.