Start with

> emacs -Q

Navigate to an octave .m file, run inferior octave. My octave file 
is:

> pkg load control
> 
> s = tf('s');
> 
> g = 1/(2*s^2+3*s+4);
> step(g);
> title ("Step response of a PT2 transfer function");

C-c TAB C-a to send to process. Graph pops up.