Puzzle : Blast fro mthe past !!!!

Professor Patrick invented a time machine. While testing it, he inadvertently reached the past. However, thankfully, he carried, in his pocket, a device that could return him to his present time. The travel to the past took its toll on him and he lost consciousness. On regaining consciousness, he found himself in an ancient laboratory, surrounded by strange-looking people. One of them seized the device from Professor Patrick's pocket. Professor Patrick tried to snatch it back but the man struck him down and let out a high-pitched, shrill laugh. He said,

"Welcome, Stranger, to the not-so-welcome land of Entropia.
I am Dr. David, the scientific plunderer from a nearby town, Enthalpia. I steal theories from other scientists and publish them as my own. Don't worry. I make sure that even their bones aren't found. (He let out yet another shrill laugh!)
It seems that this device is precious to you. I'll let you have it back if you manage to answer my question.

The people at Entropia are divided into two groups: the Newtons and the Oldtons. The Newtons always tell the truth while the Oldtons always lie.

Here are four inhabitants from Entropia: Alex, Barney, Charlie and Darren.

(Turning to Alex) Alex, is Barney a Newton or an Oldton?"

Alex replied, "An Oldton, sire."

"All right. Barney, What about Charlie? Is he a Newton or an Oldton?"

"Charlie is definitely an Oldton."

"Hmmm. What about Darren, Charlie?"

"Darren is an Oldton, Sir."

"Haha!! And, finally, Darren, if I ask Alex about Charlie, what will he say?"

"He will say that Charlie is an Oldton."

"Very well. Ok, Mr. Stranger, Now answer my question: Is Darren a Newton or an Oldton? If you answer correctly, I shall let you go scot-free. Lest, you will have to explain the secret of this device to me and prepare for a gruesome death. Muahahahaha!!"

Help Professor Patrick solve this riddle and return safely to the present time. Provide a detailed solution along with your answer.