I read this in a Swiss newspaper yesterday;
Adventszitate
“Regelmässig zum Fest der Liebe wächst meine Mordlust”
Agatha Christie.
I haven’t been able to find the actual quote in English,or when and in what context it was said or written, but roughly translated it is;
Advents Quotation
“Regularly to the Festival of Love (Christmas,Advent)
grows my urge to murder”
I would love to know what she really meant by it, but I think I understand her.
Diamonds and Rust 
Comments on: "A Quote for Advent" (1)
I’m not really sure, but given that she was one of the premier murder mystery writers of the 20th century, it might have meant that her urge to write another novel grew in proportion to the Christmas season. Christmas sales and all, you know. Just a guess.
But why would she have written that in German in the first place? One wonders.
-smith