On the UK perspective of this same “sleepers” is an excellent from a true story- US television version of “Pack of Lies” with Alan Bates and the sadly now ill with MS Terri Garr, and Ellen Burstyn -— in the real life story of the spy couple in the UK-— Morris and Lona Cohen.
https://en.wikipedia.org/wiki/Pack_of_Lies
So the UK had their own version of the Rosenbergs? Never knew about that.