The reverend mother had been absent for about 15 minutes after her baffling request, but has now returned and the reason is laid bare. Through a long and winding conversation it becomes clear that she wants to honor the wishes of “Mere Crucifixion” the sister who had recently died. That sister wished to be buried in the coffin she had slept in every night. She did not however, want to be buried in the ground. She wanted to be buried in the vault beneath the alter, a practice that had been outlawed.
It is decided that Fauchelevent, with the help of a rather large sister, will carry out this act under the cloak of darkness. The crowbar is to open the vault. The sister will be nailed in her sleeping coffin and lowered into the vault. The vault will be closed up before anyone knows what has happened. The actual coffin will be filled with dirt and carried out by pall bearers the following morning.
During this winding conversation the reverend mother agrees in theory to employing Valjean and taking on Cosette (though their names are not shared for obvious reasons). This takes care of the second half of the plan but leaves us with the big question, how will Valjean get out? There have been hints pointing us at this coffin that must leave the grounds. Will that be the answer?