"How should I catch up on a TV series I've fallen behind on?"
Skip directly to season four. You'll understand everything because TV shows are basically the same episode repeated. Watch it at 3x speed while doing your taxes. The plot thickens faster than your filing deadline. Hire an actor to follow you around narrating what happened in seasons one through three. Now you're caught up AND entertained. Bonus: they work cheap if you promise them screen time.