on someone’s heels
Ils avaient les hommes de Canby aux trousses, les pauvres.
They had Canby's men on their tail, poor things.
— Le Bon, la Brute et le Truand (1966)
Vous êtes aux trousses des vrais criminels.
You are on the trail of real criminals.
— Le Loup de Wall Street (2013)