Green’s Dictionary of Slang

(orig. US) in trouble, in a dangerous or difficult situation.

1928		Phila. Eve. Bulletin 5 Oct. 40/4: Here are a few more terms and definitions from the ‘Racket’ vocabulary: [...] ‘Put in the middle,’ to compromise [i.e. a third party].
1933		J. Spenser Limey 162: A friend o’ mine’s got himself ‘in the middle’ (into trouble) an’ I gotta get him out.
1949		Monteleone Criminal Sl. (rev. edn) 185: put in the middle To be placed in an untenable or dangerous position.
1954		‘Nicholas Blake’ Whisper in the Gloom (1959) 187: I still don’t like it. How d’ya know he’s not leaving us in the middle?
1960		E. De Roo Big Rumble 58: You’re no zero. You’re in the middle.
1972		J. Burmeister Running Scared 131: But I am the man in the middle. If your note giving my location should go astray [...] I could quietly starve to death.
1982		L. Cody Bad Company 119: Why do I always get caught in the middle?