Of course if clubs break 3-3 there is no problem as you can discard a diamond on the 13th club.  But North may well have lead from a 4-card suit - which is the case here.  There may be an option of a squeeze play if North holds the clubs and a high diamond.  Plan to lead the diamond ten, preparing to perhaps lose to a diamond honour in South's hand.  (you need to lose a diamond trick for the squeeze to work)  As it happens both honours are with North, so he should cover your ten.  Having also lost a heart and the club king, West should cash the diamond ace and run the trumps.  North can't keep all his clubs and guard the diamond king.