What should be done by a person whose wife without divorcing him married other man?
My son's wife left home 2 years ago and is staying with another man after marrying him. We have proofs of her marriage with the other man. Can we file an adultery case against her and ask the police to raid their home and arrest her for adultery?
Also, on what all grounds can we file a divorce against her?
Yes you can register a complaint in the nearest Police Station for the offence of Bigamy under Section 494 of the Indian Penal Code and for adultery under Section 497, however your son's wife shall be punished for the offence of abetting adultery.
With respect to seeking divorce,
Your son can seek divorce under Section 13(i) and 13(ib) of the Hindu Marriage Act, 1955 on the grounds of adultery and on the grounds of desertion for a period of 2 years.