english
1
general::
see UP TO, def. 3.
American Heritage Idioms
2
general::
Phrase(s): up to no good Fig. doing something bad. • I could tell from the look on Tom’s face that he was up to no good. • There are three boys in the front yard. I don’t know what they are doing, but I think they are up to no good.
McGrawhill's American Idioms And Phrasal Verbs