tom couldn't tell me the truth
->...............................................
that woman is my aunt you met her yesterday
->...........................................................
Noone can know the truth
-> the............................................
tom couldn't tell me the truth
-> I couldn't be told the truth by Tom.
that woman is my aunt you met her yesterday
-> The woman whom you met yesterday is my aunt.
Noone can know the truth
-> The truth can't be known.