This is book number 3 in the Hercule Poirot series.
Agatha Christie invented Gone Girl-ing. No, but really. After she found out her first husband was cheating on her she faked her own kidnapping and caused a nation-wide manhunt. Then she got remarried to a dude 20 years younger than her and they spent their lives happily traveling the world, blissfully in love. Living well is the best revenge.— Cristin