Before the opening credits of In Purgatory's Shadow:
(Bashir is waiting for him with a phaser.)
BASHIR: Going somewhere?
GARAK: I really must remember to stop underestimating you, Doctor. How did you know?
BASHIR: You mean that you were lying about the contents of the message? You said you'd given up on the Cardassian survivors who were lost in the Gamma Quadrant. Well, Ziyal was right. You're not the giving up sort.
GARAK: Very good, Doctor. You've come a long way from the naive young man I met five years ago. You've become distrustful and suspicious. It suits you.
GARAK: Yes, but aside from that, we were very close. He was my mentor, and I'm not going to turn my back on him. If it'll make you feel better, you can come with me. All you have to do is come up with an excuse why you need the runabout and we could leave immediately.
BASHIR: So let me get this straight. You want me to lie to my commanding officer, violate Starfleet regulations, and go with you on a mission into the Gamma Quadrant which will probably get us both killed?
GARAK: I'm ready when you are.
BASHIR: In that case, let's go. To Captain's Sisko's office.
Later in the episode we find out Bashir has been replaced by a changeling.
Why would the changeling (as Bashir) take Garak to Captain Sisko?