Friend,
You have not mentioned the type of industry you are in.
Attrition rate of 25% is quite high. Hence it has to be understood that there is something radically wrong. Have you done any sort of introspection internally among yourselves.
Are you in tune with industry standards? If so, do you provide equal opportunity for growth to your employees?
Do you have any structured growth plan for your employees?
"GRILLING" of the employees is not at all required. People on their own would open up if you have a sound HR policy with a level-headed, mature person on the top.
However, immediately you can probably conduct an in-house opinion poll wherein you can structure questions so as to get a proper inference. This must be voluntary, anonymous, and above all, the employees must be given the confidence that they will not be punished for being frank in their opinion.
By and large, this issue is not very serious and can be tackled effectively if only you have a good HR policy and an attitude conducive to growth and comparable standards in the industry.