They say in AA, you're only as sick as your secrets. I don't think all secrets are sick -- if this is a secret that you're keeping in good conscience for someone else's real welfare, then it will be ok for you to tell Sam's dad that you simply can't talk about it. You have a prior & serious confidential obligation -- when he asks you what and to whom, you'll have to (as we say over here anyway) butch it out. He might not like it but you won't be in the wrong.