Though you've got to sort of admire a woman who can single-handedly construct a 'living tomb' torture contraption and bury it underground, install victim inside, and remove all evidence of having done so, before the builders rock up next morning.
And to think we Brookside fans thought Trevor Jordache under the patio was melodramatic back in 1993.
Am completely confused as to what significance kept being underlined by all the repetition of captivity: was the take-home message something meaningful about being hostage to our subconscious? Imprisoned by our desires? 
- Childhood experimenting with ropes/ knots/ captive games etc.
- Punishment by being locked in confined spaces.
Seems a bit dubious, linking Paula and Callum's regular childhood experimentation, to that one accidental (non-fatal) strangulation, to Paula's consensual adult bondage with every adult sexual partner ("gets me in trouble, Mac"), to Crystal locking Morgan, bound and gagged, into a cupboard...
Pretty sure James's account to Mac of how Mary died was far from the truth.
(As Morgan contradicted what he'd said).
Perhaps lifestories exchanged in bed by Paula and James, were woven into each other's and Mac heard similarities from both?
Didn't explain why Mary's lips were stitched together.
Or did we call it right, upthread, that it was symbolic: she could never "speak the truth"?
Being kept challenged by some ambiguity's one thing, but...