A “plot” for your new novel? Not that it can’t be true ...
Forgot about these, did you?
https://www.theguardian.com/world/2016/sep/09/cell-of-french-women-radicalised-by-isis-behind-failed-notre-dame-attack
&
https://www.thedailybeast.com/an-isis-plot-to-blow-up-notre-dame-cathedraland-rule-the-world