The Rare Coin Score doesn't contain the greatest Parker crime caper, in fact it's a fairly uninteresting one that relies on some shoddy security for an event housing such valuable merchandise, as well conveniences of no one in a hotel noticing some unauthorised construction work. What lifts the story though is the introduction of a new character in Claire, who for those who have read books further in this great series know becomes a staple character. The scenes with Claire are far more interesting than the caper to steal a heap of rare coins from a hotel coin convention. If you've read those other Parker books you're going to want to read this adventure just to know how Claire and Parker came to be.
Basic plot, Parker doesn't need a caper, he's got plenty of money to get by from the events of the previous novel The Handle. However he's bored and doing things that are quite, well unparkerlike. He concludes he needs the challenge of planning a caper to get his mind and sanity back on track. However there's not much happening at the moment but a reliable acquaintance named Lepke who he'd worked with a while ago in the past, invites him to join in on what he claims is a sweet deal. Unbeknownst to Parker, Lempke has just come out of a lengthy stint behind bars, the others involved will be amateurs and the guy whose idea it is, is a complete social loser and coward. When a skirt turns up to take him to the meet, Parker knows doing this caper isn't probably going to be a great idea.
The next book in the series is The Green Eagle Score. Unlike a lot of other Parker novels the Rare Coin Score doesn't give away any of the plots of previous novels so you can read this as a standalone if you just want to read the book where Parker meets Claire but plan on reading the previous novels further down the track.