1. Before your ladyfriend goes out of town for five days, tell her that on the evening she comes back, you don't want her to go to karate because you want her to do something else. She will clap her hands and tell you she loves surprises and then demand to know what you have planned. Refuse to tell her, even though this will make her very angry and she will probably start complaining that she won't have been to karate in a week and it's very important that she maintains a consistent training schedule and it's probably not a good surprise anyhow so MAYBE she'll come home that evening but MAYBE she'll go to karate after all because who are you to tell her she can't go and what the heck is your surprise going to be??? Patiently tolerate all this, secure in the knowledge that no matter how grumpy she is, she'll still say yes when you ask her to marry you. Um, probably.
2. While she's gone, build an Incredible Machine in the living room:
3. Luck will be with you, because she will have gotten sick on the plane ride back and decide to come straight home after all. As you're driving her back to the house, she will ask if you brought her aspirin for her headache and want to know (not very nicely) if she'll need to dress up for your suprise, because she's really tired and feels crappy and won't be very good company this evening. Briefly reconsider the question you're about to ask her. Decide to go through with it after all, but only because some of the components that you purchased to build the Incredible Machine are non-returnable.
4. When you get inside, she will crack up at the sight of the machine, and ask, "THIS is how you spend your time when I go out of town???" Decide to interpret this as a good sign. Remember to warn her that this machine has a very high failure rate. Tell her to turn on the ceiling fan.
5. After several attempts, the stuffed monkey tied to the ceiling fan will finally hit the ball bearing, which will roll down the chutes and hit the On/Off switch of the surge protector, which will power up the clip-on fan, which will blow the roll of packing tape into the tennis ball, which will roll down the pipe and knock over the cereal box, which will pull on the twine threaded through a series of suspended pulleys, which will yank the cover off the upside-down box screwed to the ceiling, which will send the tiny clay Katie on her toy parachute with a ring on her oversized clay finger tumbling to the ground:
6. Hopefully she will say yes, because - let's be honest - you don't have a backup plan...