W. Va. Code § 56-5-9
A defendant who files a plea or account under this article shall be deemed to have brought an action against the plaintiff (at the time of filing the same) for the matters mentioned in such plea or account, and the plaintiff shall not, after the plea or account is filed, dismiss his case without the defendant's consent, but shall be entitled to every ground of defense against the defendant's demand of which he might have availed himself by special plea or otherwise in any action brought against him upon the same demand. On the trial of the issue in such case, the jury shall ascertain the amount to which the defendant is entitled and apply it as a setoff against the plaintiff's demand, and, if such amount be more than the plaintiff is entitled to, shall ascertain the amount of the excess, including principal and interest. Judgment in such case shall be for the defendant against the plaintiff for such excess, with interest from the date of the judgment till payment.
W. Va. Code § 56-5-9