card up one's sleeve
ace up your sleeve
Another help, plan, or argument kept back and produced if needed; another way to do something.
Туз (козырь) в рукаве. Припрятанный аргумент, план и предъявленный при необходимости; альтернативный путь сделать что-нибудь.
John knew his mother would lend him money if necessary, but he kept that card up his sleeve.
Bill always has a card up his sleeve, so when his first plan failed he tried another.
The manager has an ace up her sleeve. She'll surprise us with it later.
У нашей управляющей есть козырь про запас; она нас им еще удивит.