That is one of the big differences in this version is that Casey seems more important then April. She has been in the book from the first issue in the background, but hasn't done much. In fact she doesn't meet the mutated version of the Turtles to much later in the series while Casey meets Raph in the first issue. Yet finally here in her own solo issue IDW's April gets her moment to shine.
What made this issue great for me was the fact that it address's the fact that she hasn't done much. She feels like the outsider because she can't fight, and be useful like Casey can. It is still here coming to grips with the fact she has been brought into the lives of four walking talking turtles. She is also dealing with the fact that she came to work for Stockgen because she thought they were trying to help the world, and she has found a dark underbelly.
Beware that there may be spoilers below this point.
April using her position at Stockgen decides she can spy for the Turtles and try to see if they are working on a way to track them again. She swipes the card of a fellow coworker allowing her access to the inner workings. There she discovers Rock Soldiers and another Turtle Tracker. This is also where I have an issue with this issue. She runs into Chet who doesn't seem to realize April isn't supposed to be there or that it is weird at the least.
She gets the tracker and causes some chaos along the way. In the damage she causes she is chased through the lab and discovers that they are still experimenting. She doesn't look close enough to see that they are mutating other creatures though. Because of the damage she causes one of them escapes and we have our IDW version of Slash!
The issue ends with April getting away and back to the Turtles and Slash escaping the Lab. This issue seems like it fits best after #14, which isn't out yet, and before #15 which starts a story arch called Blood Brothers.
This is a great issue over all and it really gives April her moment to shine. It should be really great to see where the next storyline goes based off of this too. Another solid issue. Also the art is very well done. It is more in line with how the book was, not where it is. It should be interesting to see how some of the things introduced here look in the ongoing book though.
So pick this issue up. It is going to be one you don't want to miss.