Some of Grindelwald's fanatics (pref. unknown to Grindelwald) decide to get revenge on the motley crew who ruined their glorious leader's sneaky infiltration of MACUSA. The Auror and the Legilimens are somewhat dangerous and the No-Maj is being 'monitored' for signs of remembering magic (that's Queenie's story and she's sticking with it). The Magizoologist, though? He's obviously the easy target.

They find out the hard way (as in crash course, emphasis on crash) that they were very, very, VERY wrong.