One question I've gotten from readers about the protagonist in the Mission series is what happened to him at the Hussa facility and how is the alien material injected into him during the experiment working in his body? What is it doing to him? That is a question I plan to answer with some clarity and length in the seventh book, Phoenix Rising.
The gristone sword and Tulos's spiritual journey. he will definitely be making a big comeback along with the crew on mars Rychik and Genevieve in the last book. he will be a new man, so to speak. and a powerful warrior with a new calling. there will be an old enemy who will return in a new and frightening form for the last two books.
As for the sixth book, A Venus Affair. this si another one of those 'alien/monster-of-the-week' books in between the Big Battle coming at he end of the series. However this next book is very much related to the others when it comes to materials for a new weapon that Ellen Vartan is building against the aliens. Anyway, I feel like the series is in a good place now that I've reached the midpoint of the series. So what's coming next? After the Mission series is over I'll be writing a new scifi series. a detective series.
Think The Dresden Files with science fiction. :)