Someone Else's Shoes

I always include major spoilers (hidden), to help with my memory  issues. Read them at your peril! 
Nisha has been married for 20 years to an awful human being.
Sam has also been married for a long time to a lovely man, who has depression and is unemployed. Her boss is awful, her parents are critical and demanding,  and she's struggling to cope.
Sam accidentally picks up Nisha's bag in the gym, forcing them to swap shoes, and things go increasingly crazy from there. Life changing stuff. Good female relationships, lots going on. It all comes together very satisfyingly in the end. Nisha's husband is a diamond smuggler unknown to her. He is a ruthless and dangerous man. Sam's husband had to constantly refuse to end his dad's  life, also unknown to his wife.