Set early on in the series, as evidenced by the fact that they're still calling Danny 'InvisoBill'. :P
Class Discussion
October 9, 2011
Mr. Lancer sighed as he struggled to calm his rambunctious classroom. Ninth grade was hard enough without adding the thrill and excitement of ghost sightings. And not just any ghosts, but public enemy number one.
The ghost kid.
"Ghost Sonata, people! Stop talking about that menace to society and turn to..."
"He's not a menace, Mr. Lancer. Inviso-Bill totally saved Paulina... he's a hero!"
Danny smiled. Of all the people to stand up for his new alter-ego, he never expected it to be Dash.
Too bad the guy would beat him up as soon as he got out of class...
The Ghost Sonata is a rather interesting story by Swedish playwright August Strindberg.