This is episode 28 of 30 of Undercurrent. Play it below, then continue straight into the next episode — the whole season is free and needs no account.
The closing stretch of the season, where the arc pays off.
Jiang Xi's sister, a maid, was murdered by Lin family's mistress, Han Xue. Now, Jiang Xi, disguised as a maid, infiltrates to avenge her sister, using Han Xue's own cruel methods. She will destroy Han Xue and Lin Wendong.