I was wondering about the skylight as someone mentioned upthread, how it had been put in as a 'surprise' so maybe Kay didn't know about it (and fell through it as it was covered) but that seems a bit far fetched.
Think Kay's husband has been overly affectionate (towards Ellen) and weird all along.
I don't think Paula's husband is the baddie, unsure about Ellen's..
I really hope we have proper answers in the final. Like why on earth Kay would ask a heavily pregnant colleague who is suspended and banned from the building site, to said building site late at night. She sounded very stilted so wonder if someone was forcing her to make the phone call...