W. Va. Code § 56-5-4
In a suit for any debt, the defendant may at the trial prove and have allowed against such debt any payment or setoff which is so described in his plea, or in an account filed therewith, as to give the plaintiff notice of its nature, but not otherwise. Although the claim of the plaintiff be jointly against several persons, and the setoff be of a debt, not to all, but only to a part of them, this section shall extend to such setoff, if it appear that the persons against whom such claim is, stand in the relation of principal and surety, and that the person entitled to the setoff is the principal. And when the defendant is allowed to file and prove an account of setoff to the plaintiff's demand, the plaintiff shall be allowed to file and prove an account of counter setoff, and make such other defense as he might have made had an original action been brought upon such setoff, and, in the issue, the jury or judge shall ascertain the true state of indebtedness between the parties, and judgment shall be rendered accordingly.
W. Va. Code § 56-5-4