This is an action to recover amounts due under a contract signed and sealed by the plaintiff and defendant of the tenor following: “ In consideration of these mutual covenants and our seals hereto affixed we, Dr. Charles F. Berry and Thomas Allen, Jr., Trustee for Lorette C. Berry, agree by and with each other, as follows: — The said Dr. Charles F. Berry agrees to pay on or before the tenth day of each and every month starting September 1st, 1920, an amount equal to $30.00 per week, or $120 per month, to said Thomas Allen, Jr., Trustee as aforesaid, for the support and maintenance of said Lorette C. Berry, wife of said Dr. Charles F. Berry. The said Thomas Allen, Jr., Trustee as aforesaid, agrees to receive said amount as aforesaid and transmit the same to the said Lorette C. Berry. Witness our hands and seals the day and year first above written.” The defendant pleaded among other matters that his execution of the agreement was due to fraudulent *542conduct of the plaintiff’s cestui. The defendant made the following offer of proof: “ that under the agreement the witness Allen, under direct and cross-examination of the cestui — that at the time that that written agreement was entered into the cestui had in her possession sums of money approximating several thousand dollars which belonged to the defendant, and that at that time the defendant agreed to pay the sum of $30 per week he made the agreement with the understanding and belief that these sums should remain intact and not be used by the cestui or the trustee until the termination of the marital difficulties between them. The defendant further offers to prove that the cestui has appropriated these various sums to her own use and benefit, despite the contract entered into between the defendant and the plaintiff trustee. The defendant offers as an equitable defence the fraudulent acts and omissions and concealment by the cestui as a defence.”

The single exception is to the exclusion of this offer of proof. In this there was no error. Under G. L. c. 231, § 31, “ The defendant may allege in defence any facts which would entitle him in equity to be absolutely and unconditionally relieved against the plaintiff’s claim or cause of action or against a judgment recovered by the plaintiff in such action.” This offer of proof constitutes no defence at law or in equity to the plaintiff’s claim.. The only parties to the contract are the plaintiff and the defendant. It is under seal. Only the parties to a sealed instrument can sue on it. The wife is not a party to this contract. The facts set forth in the offer of proof do not constitute fraud such as to avoid this contract. There is nothing to indicate that the plaintiff had knowledge of the facts or was in any particular in collusion with the defendant’s wife. The final sentence of the offer is simply a characterization of the facts stated earlier and adds nothing to them. It sets out no new fact. Whatever may be the respective rights of the defendant and his wife to the property to which reference is made, no fraud is shown with respect to the contract on which the "present action is founded. The most that could be. inferred from the offer was a misunderstanding on *543the part of the defendant as to what he expected his wife to do with his money in her hands. If his legal rights have been impaired by her with respect to that property, that controversy does not constitute the defence of fraud or any equitable defence to the present action.

Exceptions overruled.