(After stating the facts.) The defendant in the court below by general demurrer challenged the right of the plaintiff to recover on the case as set forth in the petition. The court held that *857the petition set forth a cause of action, and overruled the demurrer. Under the contract in this case between the plaintiff and the defendant municipality, the former was entitled only to the sum of $1,500, for which, in a proposal offering his services to the municipality, he had undertaken to supervise the construction of the contemplated work and to see that the same was carried out according to the plans and specifications to be adopted. Under the proposition submitted by the plaintiff himself in writing,.he was to “do all the work for the lump sum of fifteen hundred dollars, this amount to include all expenses o£ getting up the plans and specifications and the supervision of the work after the same has been contracted.” This proposition was accepted by the Town of Decatur without additional stipulation or qualification. It would be difficult to conceive of a contract freer from ambiguity and more plainly revealing its meaning without the aid of construction or interpretation. As brief as the contract is, it iterates and reiterates the proposition to do the work of supervision, and to do and perform all the duties incumbent upon the engineer of such an enterprise, for a “lump sum” definitely fixed. Jaudon was not a party to the contract between the town and the firm of contractors, Walton & Wagner, and he can not invoke the terms of that instrument to change or alter the plain terms of the contract between himself and the defendant in this case. In this connection see notes to the case of Inman Mfg. Co. v. American Cereal Co., 8 L. R. A. 1140 (133 Iowa, 71, 110 N. W. 287), and cases there cited. If it were permitted by parol evidence to raise an ambiguity in a contract as free from that vice as the contract now under consideration is, then no written contract could be exempt from the danger of attack by parol evidence.. The court erred in not sustaining the general demurrer.