Returning to the game after some years, at which time the sole rulebook was Lord of the Rings: Strategy Battle Game. What is the current authoritative print I should buy?

I don't mean to sound stingy but you should really not buy anything for the time being. The current edition of the rules is in The Hobbit, An Unexpected Journey: Strategy Battle Game but a new edition of some sort is coming out in the autumn. Given the cost of the books I recommend waiting until after this new book comes out to see if it makes the current one obsolete. It might be a companion book, like Legions of Middle Earth was to the old rule book of course. Still I recommend waiting if you can.

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"Draw your sword with a heavy heart, but swing it with a heavy hand"

As devil's advocate, I recommend the small digest rulebook from the escape from goblin town. Find a spare copy online. I got mine for twenty usd.

According the Warhammer Fest seminar, sounds like the new edition of the rules will be in 2018.

If you're interested in playing with the models from the last two Hobbit films and thinking of getting the There And Back Again book, you can get that and the hardback Hobbit rules manual together for a good price: https://www.games-workshop.com/en-GB/Th ... Collection