Scientology.
Sources say the Tom Cruise-Katie Holmes divorce is happening for precisely that reason, specifically her concern that Suri will be introduced to it.
Their daughter is now six, the age where Scientology will begin to be a major part of her life, and Katie fears Suri will be dragged in too deep.
Holmes has never fully committed to Scientology, TMZ reports, despite her ties with the church and more than five years of marriage to Tom.
Many observers felt their marriage would never work for this reason; Katie respected Tom's beliefs, but raising their child his way a different story.
As she's grown, the couple had been arguing over Suri with greater frequency, and Katie eventually filed for divorce to protect the little girl.
A key detail in the Tom Cruise-Katie Holmes divorce filing was the location in which it was filed: The 33-year-old actress made if official in New York.
She does not want Tom, 49, to control decisions relating to Suri's religion, and feels N.Y. is far more likely to grant her request for sole custody.
Holmes reportedly is not after money - she had plenty before they got married and there's a prenup in place anyway - just little Suri Cruise.
Tom deeded their NYC apartment to Katie last year, reportedly for tax purposes; she's using it to establish residence, and file for divorce, in the city.
What is Scientology and is Katie right to be running scared? You will surely have plenty to say about it in the comments, but we leave you with this:
Here's Cruise describing Scientology and what the faith means to him in a video leaked in 2008. Clearly, the man takes it very seriously ...
