dà / jiā / yǐ / wéi / shì / qing / mán / de / hěn / hǎo / ， / méi / xiǎng / dào / tā / bǎ / dǐ / xì / dōu / dōu / dǐ / shuō / le / chū / lái / 。

大家以为事情瞒得很好，没想到他把底细都兜底说了出来。

Everyone thought the matter had been well hidden, but he unexpectedly exposed all the details.