under lock and key idiom
锁起来的，存放好的
locked away safely
Her jewellery is securely under lock and key at the bank. 她的珠宝全都安全地存放在银行里了。
（尤指罪犯）在牢房里的，在押的
If a person, especially a criminal, is under lock and key, they are being kept in a place from which they cannot escape, usually a prison.