modal forms

I want to display 4 modal forms at a time.
form1 call form2
form2 calls form3
form3 call form4
form4 should be the active form.
After form4 closes ,control should go to form3,then form2 and form1.
I am invoking the forms in Activate event.
But it is in infinite loop.
As the form3 activate is getting called after form4 is closed .

I need a solution wiothout using global variables.
Pl. help