I'm game

C.S. Lewis の小説 The Magician's Nephew を読み始めました。
"Why, it's the empty one. Daddy says it's always been empty since we came here."
"I suppose we ought to have a look at it then," said Digory. He was a good deal more excited than you'd have thought from the way he spoke. For of course he was thinking, just as you would have been, of all the reasons why the house might have been empty so long. So was Polly. Neither of them said the word "haunted". And both felt that once the thing had been suggested, it would be feeble not to do it.

"Shall we go and try it now?" said Digory.

"Alright," said Polly.

"Don't if you'd rather not," said Digory.

"I'm game if you are," said she.
"I'm game" ですが、この後結局 PollyはDigoryと共に行動するので、反対しているのではない事は確かです。
辞書で意味を調べます。

・Oxford English Dictionary: Eager or willing to do something new or challenging.: They were game for anything after the traumas of Monday.

・Collins Dictionary: If you are game for something, you are willing to do something new, unusual, or risky.: After all this time he still had new ideas and was game to try them.

・Cambridge English Dictionary: willing to do things that are new, difficult, or that involve risks: It was a difficult challenge, but Roberta was game.