This is the third book now in the Agatha Christie Book Club series.
From the Blurb:
It was supposed to a frivolous night out. The champagne was flowing, the rugs were arranged, and the Agatha Christie Book Club had settled in to watch their favourite mystery Evil Under the Sun on the moonlit screen above.
Yet it all comes to a crashing halt when a woman’s lifeless body is discovered lying between the jumble of picnic baskets and blankets. She has been strangled and discarded like an empty champagne bottle.