Without dropping any major spoilers it is a book length adventure for Classic Traveller detailing the Aramis subsector.
The campaign itself is built around the adventures of the subsidised merchant the March Harrier and its crew and features the theft of a maguffin, scheming megacorps, unscrupulous smugglers, rampaging Vargr corsairs, two decidedly weird alien races, a psionics institute and much more.
Given that the March Harrier is a jump-1 starship you can easily spend a year of game time on the campaign and its good for several months of weekly sessions.
At its time (early 1980s) it was considered not just the best Traveller but one of the best scenario packs ever released for any RPG.
Looked at twenty-odd years on its not without flaws: no NPC stats, only a handful of the worlds are mapped, the only deckplans given are for the March Harrier itself and some of the scenario chapters are less detailed (in current RPG terms they are more like adventure seeds than fully fleshed-out scenarios) than they should be.
Production values are pretty good for the time - its a full size softcover RPG book rather than a LBB, not a lot of art but relatively well laid-out and organised.
So it does require rather more work from a GM than equivalent campaigns for a more modern RPG.
However if you're using CT to play it, statting up NPCs etc is not a big deal - and if you're converting it to another system the lack of detail may actually be a positive.
I'd still say it's a must buy and in effect you can now get it for pennies as it is included on the new Classic Traveller CD-ROM.
If you want a dead tree copy, it does come up relatively regularly on e-bay and I think I got mine for about $30 or so.