Dragon Age II - plot point not showing on map

Hi. Am new here. Been trying to play Dragon Age II for several days now and after a few days, I had to restart as the plot point is not showing on the map. The first time it happened I thought I did something wrong so I started anew with a slightly different character. But this is like the upteemth time and I am now stuck again. 
We are doing the "The Way It Should Be" Companions' quest and is supposed to take Aveline to Lowtown at night to rescue Guardsman Donnic's patrol but when we went there, there is no plot point on the map so where do we go?

I have done the Guardsman Donnic's quest on an earlier game which I had to ditch coz we could not find the plot point for another quest.

I thought the game was not supposed to be linear.

Really need help as I am rather pissed off and cannot keep repeating the first part over and over again. It does get rather boring after a while if you have to keep reading/hearing the same script over and over again. 

Help!

Thanks.

Warmest regards,

Roowina from Malaysia