Iowa Code § 364.14
When action is brought against a city for personal injuries alleged to have been caused by its negligence, the city may notify in writing any person by whose negligence it claims the injury was caused. The notice shall state the pendency of the action, the name of the plaintiff, the name and location of the court where the action is pending, a brief statement of the alleged facts from which the cause arose, that the city believes that the person notified is liable to it for any judgment rendered against the city, and asking the person to appear and defend. A judgment obtained in the suit is conclusive in any action by the city against any person so notified, as to the existence of the defect or other cause of the injury or damage, as to the liability of the city to the plaintiff in the first named action, and as to the amount of the damage or injury. A city may maintain an action against the person notified to recover the amount of the judgment together with all the expenses incurred by the city in the suit.
Iowa Code § 364.14