Fache calls Collet to tell him what Sophie and Langdon had cooked up with the bar-of-soap trick.
Collet can't figure out why Sophie would tip Langdon off to their investigation.
On the other hand, since no alarms have gone off at the Louvre since all the officers departed, it means that Langdon (and most likely Sophie) are probably still in the Grand Gallery.
Fache and Collet send an armed Louvre security guard to go get them.
Fache's no dummy. This time he sends half his force to get Langdon at the Louvre, and the other half to the American Embassy (since that's where Langdon would head next if he knew what was good for him).