Tom postanowił wziąć sprawy w swoje ręce.

English Translation

Tom decided to take matters into his own hands.

Why is swoje ręce singular? Is this a colloquialism?

Welcome to the forums! :slight_smile:

Actually, “swoje ręce" is plural. “Swoje” is the plural non-masculine form of the pronoun “swój”, and it matches the number and gender of “ręce” here.