let in on

US /let ɪn ɑːn/
UK /let ɪn ɑːn/
"let in on" picture
1.

wtajemniczyć w, pozwolić poznać

to allow someone to share a secret or to know something that is not known by many people

:
They finally let me in on their plans for the surprise party.
W końcu pozwolili mi poznać swoje plany na przyjęcie-niespodziankę.
She refused to let him in on the secret.
Odmówiła wtajemniczenia go w sekret.