I'm pretty sure you can install steam, install the game, turn steam to offline mode, and you'll be able to play without internet from then on. Even if you are using your steam account online elsewhere. That's assuming you can get internet on the target computer in the first place.
You need internet to install steam and install the game. Which is absent on the box in this case.
But what works is this: on a machine where there is internet make a new folder, copy steam.exe there and nothing else and run and login. It starts with no games installed. If it starts installing anything, pause and delete. Install Defender's Quest. Shut down. Now you can copy the folder with steam on a pc without internet and run in offline mode.
It also turned out that there is a bug in defender quest and it
requires c++ runtime although it's not using it. So if the machine in question does not have it it hangs. At first I thought this was in my case because I was trying to run on Windows 8, but turned out, it was just because it was the very first game I put on this machine and it did not have c++ runtime on it.
In the end everything worked =)