The plan was for Bill to report a potential security breach near the Lestrange vault, which would cause Bellatrix to come and check on the Horcrux disabling any defences inside the vault. Harry would use muggle equipment to climb down with the assistance of Fleur, while Bill would smuggle Hermione into the vault. Once she had the cup, she'd replace it with a replica, and then come out to Harry and they'd hide under the cloak until security left, and then climb out the way Harry came in, up to a level where Bill had security clearance, and then he'd escort them out.

The only problem was that they'd have to wait until after the holidays. The bank was closed, and neither customers nor employees would be allowed in during this time. Hermione pointed out that that the Hogwarts Professors could take a couple days of during the holidays. Remus sent an owl to invite Professor McGonagall to come to his place, and then he met her and brought her to Grimmauld Place.

Professor McGonagall had been happy to see Harry and Hermione. She was worried that Dumbledore had trusted the fate of Wizarding Britain to three, barely of age, teenagers, rather than the Order of fully trained, highly capable wizards and witches, who each had years of experience in their respective fields. She was more worried that he had place such a heavy burden upon their shoulders, and was happy to help in any way she could.

They included her in their plans and she said she'd coordinate with the teachers and agreed to pass along a message to the DA to start preparations for the arrival of 'Phoenix' and 'Raven'. She told them that the seven secret passage ways had all been sealed, and the only way in or out of Hogwarts, where they could remain undetected, was the tunnel running from the Hog's Head to the Room of Requirement.

She told them all about the Carrows, and their so called 'teachings'. She was also able to give them the number of Death Eaters, both in and around the castle. She told them how there were a number of giants in the Forbidden Forest, and that the Acromantula Colony had almost doubled in size. She was able to point out some secret passage ways know only to the Headmaster and the Deputy Headmaster, which she had neglected to inform Snape about. They could use the combination of these passages, Harry's Cloak and the Marauder's Map to move around undetected, but first they had to break into Gringotts.

It was after that Bill, Fleur, Remus and Tonks would meet them on the Thirteenth of March to go over the two plans one last time. Harry had insisted that that two couples should take a break and enjoy their first holiday as husband and wife, and with Remus and Tonks, it was Teddy's first Christmas. When asked, he stated that he and Hermione would be fine over the holiday, just as long as no one bothered them.

Author's Note:

I don't actually know if Gringotts shuts over the holidays, but I wanted to catch up with canon, as Harry, Ron and Hermione break into Gringotts on May 1st and the Battle of Hogwarts happens on May 2nd.