Joe needed no more proof; once the token of identity was given, he realized that only The Shadow could have penetrated to this underground prison.

The Shadow penetrated farther into the suite.

He was wild with rage at the way The Shadow had penetrated into his stronghold.

Through keen ability, The Shadow had penetrated to a spot where he would dwell secure.

To those, The Shadow alone could penetrate.

The Shadow had penetrated to the power room of the swamp stronghold!

The Shadow had penetrated deeply into the case of the Yellow Door.

The Shadow had penetrated to a spot of utmost danger.

Only The Shadow could penetrate to intercept the message.

They had found a spot where The Shadow could not penetrate, and the way was closed.