Mina's discovery / Dr.Seward's disbelief

In chapter 14 Mina worried about her husbands health, she has no choice but to open and read Jonathan's Journal. She is clearly horrified by the content. She is neither discouraged or threatened, she kept strong, confident and determined to fix Jonathan's "illness" Shows she is very brave and has strong control over herself contrasting to her husband; who appears to be very weak and fragile. (A change in role)    
Van Helsing comes the next day and describes the events that lead to Lucy's death, after this Mina shows him the journal and he is VERY pleased and relieved by her actions. 

Chapter 13/15

"Radiantly Beautiful"  

The events behind Lucy's corpse for me is the Catalyst. This chapter finally gives the protagonist some hope and knowledge about the unknown antagonist. The doctors discover the coffin empty, they also believe that Lucy is the one that has wounded the children with marks in their necks. 
Dr.Seward is very reluctant yo believe that something supernatural is happening and suggest that this is the doing of a 'body-snatcher' 

As clock struck midnight Seward see a 'white streak' and Van Helsing is convinced this is all Lucy's doing.

Dr.Seward is in complete shock 'surprise and dismay shot through me' when they discovered Lucy's body back in the tomb. She appeared more beautiful than ever. "lips were red" "cheeks was delicate bloom" 
She is portrayed more in a sexual and dangerous way. With this Seward is finally convinced and decides to end her life that belongs to the 'un-dead'