Volumes 4 and 5 in this story are really more accurately 4a and 4b. Volume 4 doesn’t have an ending. It just stops in the middle of the action and continues in Volume 5 with the addition of redundant verbiage recapping what just happened in volume 4. I have never read a story that was so clearly spread out to make one volume worth of action stretch into two volumes. If you read them close together, be prepared to do a healthy bit of skimming.
I finished the series because I wanted to see what would happen. Anyone thinking of stopping at Volume 3 really isn’t missing much. I like the main characters and was unimpressed by the supporting cast who I found to be largely unbelievable and in some cases annoying, especially one that reminded me of Jar-Jar Binks.