From Longman Dictionary of Contemporary Englishbe in league (with somebody)be in league (with somebody)WITHto be working with someone secretly, especially for a bad purpose Vernon was accused by his enemies of being in league with the devil. → league
Examples from the Corpus
be in league (with somebody)• Some U.S. officials, however, suspected the chief was in league with the Arellanos.• And they reckon it's because the train drivers are in league with the robbers.• He would know from Fouché's response whether he agreed, or whether he was in league with them.• Union leaders were accused of being in league with the Mafia.• The managers carefully channelled resentment towards the county council, who, they suggested, were in league with their headmistress.• All I know is that you told Garvey we were in league with the Devil.• Some people took the religious view, boldly asserting that we were in league with the devil.• Only - was it really reasonable to think that the rest of the world was in league against him? 