They get to the tomb and open the coffin. It's empty.
Van Helsing tells Arthur and Quincey that they've opened it twice before—the first time it was empty, the second Lucy was there, looking intact (undecayed).
They go back outside and wait.
Van Helsing puts a communion wafer in the door of the tomb so that vampire Lucy won't be able to get in.
Cultural context note: Communion is an important ritual for almost all branches of Christianity. In it, people eat a piece of bread or a wafer blessed by a priest, and (according to Catholic doctrine) it is transfigured into the body of Christ. So the "Host," as the blessed wafer is called, is one of the holiest Christian artifacts out there. Van Helsing had a communion wafer with him, just in case, and it's a good thing, too.
After a while, Lucy shows up.
But it's not really Lucy; it's vampire Lucy. She's all voluptuous and sexy, but in a creepy way.
She's carrying a child, but when she sees the men, she tosses the child onto the ground.
She calls to Arthur, and he almost goes to her, but Van Helsing stops him and holds up a crucifix.
She goes to the tomb, but can't open it because of the Host (communion wafer).
Van Helsing asks Arthur if he can "go on with his work" (i.e., he's looking for permission to decapitate vampire Lucy).
Arthur is understandably shaken up, and tells Van Helsing to go right ahead.
Van Helsing removes the Host from the door, and vampire Lucy slips under the door like magic.
Van Helsing puts the wafer back to keep her trapped in the tomb. He says that they'll come back that afternoon to deal with her.
Dr. Seward's Diary, September 29
They go to Lucy's tomb and find undead vampire Lucy lying there.
Van Helsing pulls out a three-foot-long stake and a hammer.
He assures them that once they finish, Lucy's soul will be free, and she won't be able to create more vampires.
He asks which of them should set her free.
Of course the job falls to Arthur.
He picks up the stake and hammer and whacks it into her heart.
Vampire Lucy freaks out in the coffin as Arthur stakes her. Eventually she stops struggling.
She looks like normal Lucy now.
Van Helsing sends Quincey and Arthur out of the tomb so that he and Seward can cut off her head and fill her mouth with garlic.
Once they all meet up outside again, Van Helsing tells them that they still have another vampire to kill: Dracula.
They plan to meet at Seward's house in two days, along with Jonathan and Mina (whom the others haven't met yet).