make a clean breast of

Kazuo Ishiguroの "The Unconsoled" を読んでいます。

I began to walk again, this time more purposefully. After a moment, to my satisfaction, I heard her footstep pursuing me.
'Are you really not angry?' she asked, catching up.
'Of course I'm not angry. Why should I be?'
'Can I come too? To this movie?'
I gave a shrug and continued to walk at a steady pace. 'Please yourself. You're perfectly welcome.'
Sophie grasped my arm. 'If you want, I'll make a completely clean breast of it. I'll tell you everything. Everything you want to know about...'

慣用句と思われる "make a clean breast of" を調べます。

・Oxford English Dictionary: to tell the truth about something so that you no longer feel guilty: He made a clean breast of everything and admitted taking the money.
・Collins Dictionary: to confess everything (of which one is guilty): You'll feel better if you make a clean breast of it
・Vocabulary.com: admit or acknowledge a wrongdoing or error: “I do,” Lawson said, adding, “I want to make a clean breast of it.”