DS -9 :

An alien took over Bashir's body and was plotting to steal a shipment of ... stuff... to prolong his life.

The crew figures out that Bashir was taken over and they stop the bad alien dude,and at the episode's end, everyone is happy again.

I am NOT a big fan of "Alien takes over a crew member "episodes.

"I offer you a Vulcan prayer, Mr Suder. May your

death bring you the peace you never found in

life." - Tuvok.