There is a plot apparently, but it's unnecessary. Trap your enemies in your bubbles and then burst them. Don't touch the bad guys and do that for 100 levels!
This port for the Spectrum Next is virtually arcade perfect. The main difference is that the audio had to be redone on the Spectrum Next's AY chip.
Special features include a menu for redefining your controls, selecting a joystick type, in addition to difficulty level options, number of lives, scan-lines and switching between 50Hz and 60Hz.
Note that this release requires the original arcade machine ROM files which are NOT supplied. You must own them yourself and follow the instructions in the web site link in order to build the game file. We cannot tell you how to obtain these.
This work is respectfully dedicated to the original arcade game, and all those who worked to create it.