Orphan Black had this thing it did very well, partially due to Tatiana Maslany being awesome, where one of the clones would pose as a different one.
We see that in three ways for this episode.
First is the obvious one: Sarah continues to pose as Beth, investigating the German’s clone’s murder without letting anyone know she isn’t Beth. It’s touchy, and there are problems when Sarah realizes the knife she pulled off Helena has a fish on its handle. Cosima, in full on researcher mode, tells her the fish has a religious connotation where certain die-hard Christian types would find the clones to be abominations, and that having and training one (Helena) to hunt down and kill the others makes a lot of sense. At that point, Sarah notices the woman Beth “accidentally” shot and killed had the fish on the back of her neck, so maybe it wasn’t so accidental.
Second, Helena comes to the police station, her hair tucked into a hat, and also poses as Beth, leaving Sarah some nasty surprises, including a confessional video on the computer where “Beth” claims she killed the woman on purpose, and asks Paul to come pick her up. Helena seems wrong to do it, but it’s enough to fool people. It gets Sarah in more trouble when she comes back, but she handles it by…quitting the force. Hey, whatever works.
And finally, Alison has to pretend to be Sarah to make sure Mrs. S continues to allow Sarah to see Kira. That’s initially played for pure comedy. Alison has a history with community theater and tries a My Fair Lady style attempt at Sarah’s accent. Felix, acting as a coach, finds the whole thing exasperating. Alison, meanwhile, is surprised Sarah has a biological daughter (her own kids are obviously adopted). Why? She doesn’t say. Alison’s rather ridiculous attempts to get to see Kira do somehow fool Mrs. S, but Kira herself sees through it in an instant.
The episode also ends with Helena confused as Sarah put it through to the Ukrainian clone that Helena may not be the original. She collapses in an alleyway where a van with the fish logo swings over to pick her up.