I have bought a second hand copy of the above game from ebay and one card is missing.

It is a green adventure card, so I am not sure how important it could be.

Can anyone advise if this could lead to the game being unplayable?

Looks like the card is an Event card that is missing - 'Like animals before a storm'.

Without this, is the game is broken?

Missing an Event card is worse than an Encounter (since Events have the sunburst the refresh gems), but honestly, don't think you'll even notice it's not there. Especially once you add in 1, 2, 3, 4+ Challenge card expansions .

That's great, thanks.

Now I just have to buy some of these espansions, and more importantly, play the game before a new version comes out.

With the base game and most expansions out of print 'I can feel it in my water' thatthey have a new version planned.