Hi Clint,
You still have the same issue with this reworked logline. We still don't know who the protag is - the father or Frank? Who are we spending the most time with? Whose story is this?
By the way, it's recommended to avoid proper names and give us a sense of the character instead. Who is Frank? A retired cop? The father's estranged brother? "Friend" is too bland...
While his older brother frantically searches for his missing son, a [appropriate adjective] holds down the fort at home, unaware that another presence is in the house with him.
Totally lame, but you get my point - Story A is with Frank in the house and story B is the father searching for his son.
If you can provide a brief synopsis, we may be able to better provide feedback on how to tweak the logline.
Cheers,
Monique