Is there going to be another book in the Medusa Project after double-cross?

Yes there is. At the end of the book Double Cross it says "more in... Hit Squad" meaning there is going to be a sixth medusa project book. Thus book is going to be released around March 2012. However Sophie Mckenzie said that Hit Squad is going to be the final book and she is thinking of writing it from a varied perspective but is still unsure.

I hope this was helpful to many people :)