Watched series 1 & 2, then couldn't view series 3. Now it has appeared but only for a fee. Is this because it's fairly recent? Is there a standard time to wait before stuff is free, or is there no set pattern? Really kicking myself now....just seems weird to pay for it. Have held out so far but really didn't understand the cliffhanger at end of series 2 so it's bugging me. Not fishing for spoilers either 
Am new to amazon prime, only signed up for a free trial