Losing values on Recursive Exit

Hi,

I am running a pathing routine and summing the Cost:

path(Start,Finish,C2) :- 
next(Start,Next,Finish,Cost),
C1 is C2 + Cost,
path(Next,Finish,C1).

Once I hit the base case:
path(Finish,Finish,Cost).

I exit out of the recursion stack. Debug reports my C1 variable is regressin
g backwards 10, 7, 3, Unbound.

How do I save the value off the recursion stack?

Please help.

Thanks,
xanthu