An accidental portaling causes Ensign Boimler, of the USS Cerritos, to travel back in time to Pike's Enterprise. Boimler is ecstatic to meet his heroes, but they are more concerned with him not screwing up the timeline. 

 

An attempt to send him back is thwarted by Orion scientist/pirates who steal the portal. Once that's back, a second attempt is thwarted by Ensign Mariner coming through to rescue Boimler -- using up the last of the specific element the portal needs to work.

 

Cerritos/Enterprise mash-up ensues. Orion hurricanes, Vulcan laughter, and a whole lot of shenanigans.