I'm concerned about some of the posts above which seem to suggest that MCESaint should drop everything right away and go get his son, and that this is what a parent who "puts the child first" would do. I doubt that it's that straightforward. MCESaint sounds like he's got the background and the knowledge to be strategic about how to ensure that his son is safe. I'm also a single parent in a profession where I can't just "drop everything" and wash dishes or wait tables in order to be home for my child. I could, but then there'd be no roof over our heads. It's got nothing to do with "putting my child first" (or second, or last).
Also bear in mind that if his kid is in the care of a legal guardian, like AW, or someone she has designated, MCESaint may not be able to just show up and take the child home. He may be legally constrained from removing the child from the care and control of a custodial parent (which she is, as long as MCESaint doesn't have sole custody).
Calling the police would only raise the drama quotient because the child hasn't been abducted - unless there's a court order which is police-enforceable, they'll see a family dispute and a child who is with a parent, and leave it alone.
Getting advice from a family lawyer is probably the best option here, in terms of finding a course of action which doesn't prejudice any future actions in family court concerning the custody and residence of the child.