Just gathering some Blavatsky links here.
First a repeat: the Blavatsky Collected Writings.
Second: Her letters - the ones she Blavatsky before going to India.
Third and not least: Read about her life 'the Extraordinary life of H.P.B.'.
If you don't want to read that, read this about her life: Helena Petrovna Blavatsky.
Then her most famous book: The Secret Doctrine by H.P. Blavatsky.
