Thanks everyone for your suggestions. Ivy League it is. As for "where 10 may have been active" could refer to Q10, which is plum maybe?? I have thought Victoria for that. That might tie in a university somewhere!!
Here is my best shot for "Where 10 may have been active" is LIBRARY.
All universities have a library and The Library is one of the locations in Clueedo where Professor Plum may have carried out a murder (i.e. 'been active').