Headmaster Mr Cromwell is trying to clean up the school, a task made more difficult by the "help" offered by Potter. To make matters worse Potter asks Gobber to assist him in separating materials to be incinerated and those which are not. Gobber - not the best-informed at any point - is given no guidance by Potter and even dangerous chemicals are sent for burning. When Price realises this he concludes the school is at imminent risk of explosion,...
Typically for Series 4 this is not the greatest story but it does allow for some interesting sights as we see large numbers of pupils charging around the school corridors in panic and then them assembled "outside" (actually a studio backdrop but a change of scene nonetheless), film of a fire engine arriving at the school and even some special effects. There are also some scenes in Potter's boiler-room where the incinerator is based. These all provide variations on the standard classroom situations or corridors with pupils walking down them. In a sense this is the show's "disaster movie" and the scenes of panic and changes of scene do add to the rather basic story.
We also see early on that the unfortunate Miss Petting is completely out of her depth, not just reduced to tears by the pupils but even sent out of the class by them because she was talking too much! Later on when the school is evacuated we see her carried out by the charging pupils. The good-natured Mr Smith and Mr Hurst offer their help but clearly Fenn Street seems too much of a challenge for such a diffident teacher. The character of Miss Petting (played by Vivienne Martin) is a rather different teacher to those seen before and is a useful addition to the cast.
Another interesting scene occurs when Mr Smith tries to rescue some of his geography models wrongly sent to be incinerated and he is in the boiler room with Celia and Daisy. These two pupils had barely featured earlier in the episode (or much since they arrived) and it is good to see more of them. Daisy does most of the talking and she mentions about Celia's Indian heritage, something briefly covered in other episodes. Although non-white faces regularly featured among the pupils this was almost always as non-speaking extras so a little more focus on cultural and ethnic issues was welcome.
We also see how class ringleader Terry Stringer is unable to function without the thuggish Gobber's support. This marks him out from the earlier Eric Duffy who was the class leader but never needed to rely on anyone else for his power. Gobber though receives much the most screen-time and as another reviewer stated this is bewildering given how poor the character is - if this were not evident to the producers it seems really surprising. The new cohort of pupils didn't generally have much to offer but the others had a little more potential with the character of Daisy (Rosemary Faith) the best comic presence and certainly under-used.
Overall this is again far from vintage "Please Sir!" but at least the episode offered some variations in style and perspective.