Em & Jules Case 3: The Texter

From the Publisher:

After Em receives some cryptic texts, the newly named “M Crew” has a serious mystery on their hands, especially when the school’s electronic systems go haywire. With classes in chaos and grades changing by the second, the group is tasked by the student council president to find the culprit. And, with an old friend of Kyle’s offering warnings to Em and Grace framed for the crime, Em’s life seems to be coming apart at every level. In the end, the M Crew must outsmart one of the craftiest culprits around before it’s too late.