If someone has left your gaming group, but you want them to return, make sure you tell them some details of the action in the game that they've missed, but not everything. In particular, tell them about tricky and dangerous situations the PCs got into, but not how, or even if, they prevailed.

Transcript

GM: Okay then, let's start.
Anakin: <sigh> So Jim—
R2-D2: Thesis.
Anakin: Did he say—
R2-D2: Thesis.
C-3PO: So what's been happening?
Obi-Wan: Um, well, Jim and Annie are—
C-3PO: No, silly! With the game!
R2-D2: Hasn't Ben filled you in?
Obi-Wan: I've only told her stuff that Yoda would—
C-3PO: Teeeellll meeeeeeeee!!!
R2-D2: Well, I scored myself a sweet space dreadnought. Two previous owners, needs a little work.
Obi-Wan: We rescued Chancellor Palpatine in a daring raid and barely escaped with our lives.
Anakin: We visited justice upon the traitorous Sith Lord, Count Dookû.
Obi-Wan: And defeated Nute Gunray's new general, an insane cyborg called Grievous.
Anakin: An abomination. He's more machine than man, twisted and evil.
Obi-Wan: And we were shocked when we found out that he used to be—
C-3PO: Chancellor Valorum! Well duuuh!