I've never used a marriage of convenience plot before and I have discovered that there is an excellent reason for this.
I am terrible at them.
So I'm about a heartbeat away from tearing up my hero and heroine's marriage certificate. But on my quest to make a plot work (that clearly doesn't) I discovered a few tips that I wanted to share with anyone who is looking to use a MOC plot device in their books.
By making the hero and heroine strangers you can automatically amp up the tension. My hero and heroine lost their tension after their marriage and getting rid of their history did bring it back in a big way but that's not the story I wanted to tell and my characters would have to become different people.
You want to ask your hero why he has entered the marriage of convenience. Does he need money? Is he in love with someone else and no longer cares who he marries? Is he doing the heroine, or someone else, a very big favour?
You need to ask your heroine the same question. Has she married for children, safety, etc. The heroine's motive reflects on the hero, because he must be able to provide the protection, money etc for the heroine.
So now you have your motivations and you're ready to go, right? Alas, if it were only that simple. Here comes the fun part. You need to deconstruct your hero and heroine beyond their rationale. If you're me, say hello migraine.
Whatever their motivations the hero and heroine have married for something other than love. Your heroine may have married for money but if she's a romantic at heart her motive won't match her person and you'll need to dig deeper. For example, perhaps the heroine needs the money for her sister's cancer treatment and has no intention of taking a dollar more than she needs and perhaps is even planning on paying it back. Instead of a scheming gold-digger she becomes a selfless, caring woman and we all like her much better.
It's such a shame my hero and heroine won't cooperate. I can't find a strong enough conflict to drive the story. My hero wants revenge and is blackmailing my heroine into marriage, although he's not the marrying type. The hilarity of this is that it's a double edged sword and the hero is also punishing himself. He's an intelligent man so I can't really justify this stupidity.
I need chocolate.