It's a familiar story:

It started with a goal.
Jack and Jill went up the hill to fetch a pail of water.

Then tragedy struck.
Jack fell down and broke his crown.

Sometime gymnastics pays off.
Jill came tumbling after.

Yes, I used an alternate meaning for tumbling than the original story intended, but you get the idea, and I saved Jill's life by letting her avoid cranial trauma and land on her feet at the bottom of the hill. 

The topic sentences did a good job of preparing the reader for the action without giving away the story.  That is the same effect for which you need to strive

If your instructor doesn't ask for topic sentences, then you can suit yourself.  Sometimes, they won't help.