After seeing today's US episode I think the raaz is that Saxena had an affair with a woman who became pregnant and was blackmailing him. Saxena asked Neha's dad for a favour to i think take care of that lady.
The lady i think had an accident or something Neha's dad told saxena that the lady and the child are dead .
But in truth i think neha's dad might have adopted the child who is neha and neha's mom might be knowing the truth . that's why she was advising neha not to go against saxena.
Amarnath does not know about this.