From Longman Dictionary of Contemporary Englishbe on the trail of somebody/somethingbe on the trail of somebody/somethingto be trying to find someone or something by getting information about them industrial spies on the trail of technological secrets Police believe they are hot on the trail of a drug-smuggling gang (=they are close to finding them). → trail
Examples from the Corpus
be on the trail of somebody/something• Especially if you consider he was on the trail of the man he believes had his family abducted and almost certainly murdered.• He was on the trail of a stag, which turned to face him.• Cutler and Johnson are on the trail of the killer.• It had not occurred to her that the newspapers might still be on the trail of Puddephat's widow. 