What are the main ideas for And Then There Were None Chapters IV - VII?

Chapter 4 - The characters realize that their host knows a
lot about them.   Each character explains what really happened to cause the death for
which they are accused. Each character feels exonerated . The only character who would
not speak was Ms. Brent. Ironically, Anthony Marston toasts to crime at the end of the
chapter and dies.

Chapter 5: They determine that Anthony
Marston was poisoned and remove his body to his room. They all retire to their rooms. 
Justice Wargrave, General MacArthur, and Vera Claythorne all think about the murders
they have been accused of committing. Mr. Rogers, the butler, notices that there are
only nine china figures left on the table.

Chapter 6: Dr.
Armstrong thinks about the death he caused and then is called to minister to Mrs.
Rogers, who died during the night. Mrs. Brent says it was because she was guilty. The
boat doesn't arrive to pick them up, and General MacArthur predicts that they will not
leave the island. Mr. Rogers shows Dr. Armstrong that now there are only eight china
figures.

Chapter 7: Vera Claythorne and Emily Brent walk
the summit in search of the boat.  Emily tells her story, and Vera is shocked by her
hardness. Dr. Armstrong and Philip Lombard take a walk and consider the possibility that
the Rogers did kill Miss Brady by withholding medicine.  They discuss the missing china
pieces and the poem "Ten Little Indians" . They discuss the meaning of Soldier Island
and the name U.N.Owen (Unknown ---as in Unknown Soldier)   They decide to search the
island for their host.