set upon by two ogres

Kazuo Ishiguro氏のThe Buried Giantを読んでいます。
'It seems earlier today one of the village men came back out of breath and his shoulder wounded, and when prevailed upon to calm himself told of how he and his brother, together with his nephew, a boy of twelve, were fishing at their usual spot by the river and were set upon by two ogres.
"set upon" は知らないフレーズなので辞書を見ます。
・Collins Dictionary: If you are set upon by people, they make a sudden and unexpected physical attack on you.: We were set upon by about twelve youths and I was kicked unconscious.
・McGraw-Hill Dictionary of American Idioms and Phrasal Verbs: to attack someone or something violently.: The dogs set upon the bear and chased it up a tree. Bill set upon Tom and struck him hard in the face.
"attack" なら誰でも知っている単語ですが、"set upon" の様に簡単な単語から成る連語が意外と難しいのです。