Well done for taking notice of the fact that the plaintiff did not attach the original contract to the Summons/Complaint.
Now you are off to a good start. Google your state’s rules of trial procedure.
Look under ‘written instruments’ or ‘pleading special matters’ and look again for either ‘written instruments’ or ‘pleading and proof of written instruments’. This is hard because everyone lives in different states and I have no clue what your state has this under, so look hard and see what your court requires to be attached to the complaint in order to sue.
In Indiana I would find this under ‘Indiana Trial Rule 9.2′ which states:
(A)When instrument or copy, or an Affidavit of Debt must be filed. When any pleading allowed by these rules is founded on a written instrument, the original, or a copy thereof, must be included in or filed with the pleading. Such instrument, whether copied in the pleadings or not, shall be taken as part of the record. When any pleading allowed by these rules is founded on an account, an Affidavit of Debt, in a form substantially similar to that which is provided in Appendix A-2 to these rules, shall be attached.
So I would know that in order to sue me for a credit card contract they were supposed to attach the original or copy of the contract they are suing me for.
If they did not, in Indiana, I can file a Motion to Dismiss in lieu of an answer. How do I know this? I read my Indiana Trial Rule 6 which states:
(C) Service of pleadings and Rule 12 motions. A responsive pleading required under these rules, shall be served within twenty  days after service of the prior pleading. Unless the court specifies otherwise, a reply shall be served within twenty  days after entry of an order requiring it. The service of a motion permitted under Rule 12 alters the time for service of responsive pleadings as follows, unless a different time is fixed by the court:
(1) if the court does not grant the motion, the responsive pleading shall be served in ten  days after notice of the court’s action;
(2)if the court grants the motion and the corrective action is allowed to be taken, it shall be taken within ten  days, and the responsive pleading shall be served within ten  days thereafter.
So check your court rules to see if you can as well. Instead of answering the Summons in Indiana I would write up a Motion to Dismiss for failure to comply with Trial Rule 9.2.
Now check and see if the plaintiff broke one of the trial rules and see if you can file a Motion to Dismiss in lieu of an answer. Write up your Motion to Dismiss if it is allowed by your court.
It should get granted without prejudice. It would not get dismissed with prejudice at this time because the Plaintiff is allowed to amend their complaint to comply. This means that it wouldn’t be fair to dismiss a case with prejudice without allowing the other party a chance to fix their error.
The court grants the Motion, the plaintiff must then file a Motion for Extension of Time to correct the error. That too will be granted. The court will then give the plaintiff a number of days to amend their pleadings. If the time has lapsed and the plaintiff failed to do so, you might want to consider leaving it be, or seeing if you can then file another Motion this time with prejudice for the plaintiff failing to amend their pleadings within the reasonable time allowed by the court’s order.
All states are different but these are your rights. Your court rules explain everything that is needed by the plaintiff as well as your rights in order to defend yourself.
If your court does not allow a Motion to Dismiss in lieu of an answer, remember to answer your Summons anyway and put down as an affirmative defense that the plaintiff failed to attach the contract.
Regardless if this gets to trial or not, you know the plaintiff is going to have to come up with that contract. And if this is a junk debt buyer or collection agency, the chances are slim to none that they won’t have it. Keep asking for them to produce documents until you win.
If they have attached an Affidavit of Debt signed by one of their employees and not the original creditor, check your state’s evidence rules and look under what is considered ‘hearsay’ in your state. You most likely will be able to file a Motion to Strike the plaintiff’s Affidavit of Debt as being hearsay.