The idea of this episode is not too bad. Another changeling shows up that, just like Odo, is one of those 100 that were sent as younglings across the galaxy to gather experience and explore other species. Because this new changeling already lived for over 200 years he has lived a long time among humanoids and has developed a deep aversion for them. He tries to convince Odo to come with him and search for other changelings. He also tries to manipulate Odo in telling him, that humanoids just hold him back, that they fear his presence and that Odo should become what he is meant to be.
When Laas, the other changeling, provokes a fight with two Klingons, he shapechanges a sword in his hand and stabs one of them to death. While the Klingons demand his extradition and a trial and also Sisko agrees on that, Odo has a completely different view. And this is where this episode goes downhill and I started to hate Odo - again. For Odo this is just a matter of self-denfense. Not Laas but the Klingons provoked the fight. Why Laas had to kill one of them though even when they were no threat to him (they were unable to stab him) is unclear. Odo does not want to press any charges and rather accuses Sisko to be biased because Laas is a changeling.
On the one hand, they portray Odo as a man of justice, neutral and honest. But on the other hand, Odo bends justice as he wishes if only it meets his own agenda (same thing when he helped that one murderer escape and reunite with his daughter in another episode).
Also, why comes that the changelings we see are all terrible in shapeshifting faces and have some sort of lifeless masks as faces when in another episode Bashir has been replaced by a changeling and this one got his face right perfectly. Or the one that mimicked O'Brien on Earth to speak with Sisko. And later in Picard we also see changelings infiltrating Starfleet by perfectly morphing their appearances. Especially this one changeling, that lived for over 200 years. Shouldn't he be just perfect in shapeshifting faces? He is even able to shapeshift into fire or fog which Odo can't!