The defendant must also consider whether there are other people who are responsible for some of the loss, or whether the defendant has a dispute against the plaintiff. If so, and the defendant wants to get money or other judicial relief, the defendant must file a cross-complaint. A cross-complaint is nothing more than a complaint, except it is filed in the same action as the complaint. Besides the difference in names, a complaint and a cross-complaint are identical. The person served will have the opportunity to answer or demur just as a defendant would with a complaint.
Cases often have multiple parties.
As a result of the complaint alleged against the plaintiff, the plaintiff may have rights or claims against some third person, and may file a cross-complaint to assert those. The terms simply mean that there are complaints which have been filed after the complaint was filed. This does not mean that discovery and investigation cannot proceed beforehand. Indeed, they should. However, in our experience we find that many of our clients do not understand the need for and advisability of discovery, or their responsibilities to respond as well.