Can't get non-members of a group in many-to-many
===

I have two tables; one for groups, another for members.  A third table is an intersection table for members of groups, but we don't see that table when we use the entity framework.  I want to use C# and LINQ to get all the members that are not in a particular group.  I want to list these members so the user can select additional members for the group.  I can't find an example of syntax to make this work.  I am new to C# and LINQ, but well versed in SQL and VB.  Can anyone provide an example?