Having a dynamic field without a workflow or event receiver

To make things more clear: I have 2 lists, events and people.

I am creating, dynamically, a list that is supposed to take values from both lists. It's pretty simple but the complicated part is: the second field in the dynamically created list is determined by the value of the first field (which is a lookup field).

Basically, I need to populate a field after a certain field is populated.