on the trail

*on the trail (of someone or something)

 and *on the track of someone or something
seeking someone or something; about to find someone or something. (*Typically: be ~; get ~.) I'm on the trail of a new can opener that is supposed to be easier to use. I spent all morning on the track of a vendor who can meet our requirements.
See also: trail
References in classic literature ?
In the summer-time Indians might be met with at the mouths of the Stewart and White rivers, at the Big and Little Salmons, and on Lake Le Barge; but in the winter, as he well knew, they would be on the trail of the moose-herds, following them back into the mountains.
Then the drifting shadow of a huge butterfly attracted his attention, and soon he was nosing through the jungle on the trail of a wood-rat.
She did not doubt that the young fellow had already passed her sister on the trail, but, from bashfulness, had not dared to approach her.
About eleven o'clock in the morning, a great cloud of dust was descried in the rear, advancing directly on the trail of the party.
Once, he tried ninety, but collapsed on the trail and was seriously shaky for a couple of days afterward.
Let us push deeper on the trail, and if nothing offers, we must go back to the plain and strike another scent.
One night, after a somewhat sound sleep induced by hard travel on the trail that day, Tom awoke to hear some one or something moving about among their goods, which included their provisions.