Class 4-3 are in
the middle of a science lesson, and Professor Washu has a particularly
dangerous experiment to perform. She picks on Sasami to come and mix
some chemicals, then retreats to a safe distance (outside the classroom)
while Sasami adds a drop of glycerine to the mixture. The result is
an explosion that lays waste to much of the classroom, and Washu tells
Sasami that she must clean up the mess after school. Of course, this
is just Washu's not-so-subtle ruse to get Sasami alone.
Washu
puts stage two of her cunning plan into action while Sasami is cleaning
up the classroom. She complains that because "someone" destroyed
all the lab equipment, she cannot test her experimental growth accelerator
potion. She asks Sasami to test the growth formula instead, and forces
her to agree by presenting her with the bill for all the broken lab
equipment! Sasami knows that she has no choice in the matter and reluctantly
agrees. Once connected up to Washu's monitoring equipment, she drinks
the potion and within moments it begins to take effect. In seconds,
Sasami's body grows into that of an adult. Sasami is impressed, but
suddenly realises that her parents are likely to freak out at the sight
of her and begs Washu to change her back. Luckily, the effects of the
growth formula are temporary, and few seconds later Sasami reverts to
normal again. Washu is peeved that her experiment was only a partial
success, and Sasami tries to make her escape before Washu tries anything
else on her.
The
next morning, Sasami wakes up to discover that Washu's growth formula
has had an unexpected side-effect; she has changed into a baby! She
heads next door to try and see Washu, but there is no answer, meaning
Washu must already be at the school. Sasami has no choice but to walk
(or rather, crawl) to school to find Washu and get her to change her
back.
At school, Washu
is astonished to discover the side-effect of her growth formula, but
assures Sasami that she should change back to normal soon - or if she
doesn't she will look after her! Washu sends Mihoshi a note excusing
Sasami from lessons and confines Sasami to the sick bay.
Later that day,
Misao, Hiroto and Kenji drop by to visit Sasami. Sasami panics and hides
under the bed covers so her friends cannot see her properly, and tells
them that she has "an owie in her head". Washu quickly covers
up Sasami's baby talk by explaining that Sasami's headache has made
her act childish. She then quickly shoos everyone out of the sick bay
before they discover what has happened to Sasami. However, when Washu
returns, Sasami has gone, leaving a note telling Washu that her help
is not appreciated. Washu dashes off to find Sasami, but for once Sasami
has outwitted the self-proclaimed genius by hiding inside the pillow!
As Sasami's friends
walk back to class, puzzled about Sasami's condition, Rumiya lands in
a tree outside the window and hypnotises Misao once again.
Meanwhile,
Sasami decides it would be best to hide until the growth formula wears
off. She crawls to her shoe locker, hoping to hide there, but Pixy Misa
suddenly turns up. As Sasami tries to hide, Ryo-ohki pops out of a shoe
locker carrying Sammy's baton and tells Sasami to transform. Sasami
is worried about facing Misa in her current state, but Ryo-ohki assures
her that since she has won every week so far, this week should be no
different.
Sammy steps out
to face Misa, but her diminutive stature means that Misa can knock her
down easily. Sammy suggests that they forget about fighting for once,
but Misa is never one to play fair, and summons Baby Goods Girl, her
newest Love-love Monster. Baby Goods Girl manages to pin Sammy down
and subdue her with a baby bottle. For once it seems that Misa has got
her rival beaten, but luckily help is at hand. Washu turns up and gives
Pixy Misa some of her growth formula. 
Just
as Sasami did, Misa grows to adult size, but once again the effects
are temporary and seconds later she also turns into a baby. Not only
has Misa shrunk, but her Love-love Monster has as well! Freed from Baby
Goods Girl's attack, Sammy can fight back. Alas, her baton is too heavy
to wield, but Ryo-ohki has already come up with a plan. He has borrowed
the line marker trolley from the school sports field so Sammy can use
it to support her baton. Misa and her Monster make a run for it, but
Sammy pursues and casts the Baby Coquettish Bomber spell, wiping out
Baby Goods Girl. Misa is carried away from the school by Rumiya.
After school, Sasami
waits at Washu's house for the growth formula's side effects to wear
off. Night has already fallen and Sasami is still a baby, but Washu
assures her that she should be returning to normal very soon!
