An unwelcome inheritance split
Barbara leaves money to Bruce and the house to Dennis, provided Frank never enters. Dee receives nothing.
Supporting source ↗CASE FILE · S03 E03
Dennis and Dee's Mom is Dead
S03 E03Photograph not available
Dennis and Dee's abrasive mother has died, and the bad news is that she stiffed them in her will, leaving all her money to her humanitarian paramour, Bruce Mathis. But at least Dennis got her house. It's a "party mansion," and that's how he intends to use it.
THE SHORT VERSION · SPOILERS AHEAD
INSIDE THE CASE.
Recruiting a new crew
The men recruit friends with a badly shaped flyer. Charlie bonds with Ernesto over Dee’s diary.
Supporting source ↗The Seamus grift
Frank poses as Dee’s fiancé to recover the money. Bruce recognizes him and tests their commitment.
Supporting source ↗A camera becomes evidence
Bruce takes Dennis’s wedding footage as proof that Frank entered the property, threatening Dennis’s inheritance.
Supporting source ↗THE EVIDENCE
THINGS IN THIS EPISODE.
Characters
Bruce Mathis1 other recorded episode
Bruce conducts the ceremony and reveals that he recognizes Frank.Source ↗
Charlie Kelly180 other recorded episodes
Charlie opens Dee’s childhood diary in the family house.Source ↗
Dee Reynolds179 other recorded episodes
Dee stands in a white dress and veil at the garden ceremony.Source ↗
Dennis Reynolds176 other recorded episodes
Dennis records the ceremony on a handheld camera.Source ↗
Frank Reynolds171 other recorded episodes
Frank wears a patterned shirt while posing as Seamus.Source ↗
The Lawyer6 other recorded episodes
The Lawyer reads Barbara’s will to Frank, Dennis and Dee.Source ↗
Locations
Dee’s apartment29 other recorded episodes
Frank and Dee sit with Bruce’s children in her living room.Source ↗
Paddy’s Pub147 other recorded episodes
The gang examines a set of knives at the bar.Source ↗
The party mansion2 other recorded episodes
The large Reynolds house becomes Dennis’s proposed party venue.Source ↗
Objects
Camcorders17 other recorded episodes
Dennis films the wedding and its confrontation.Source ↗
CrossbowsOnly recorded here so far
Charlie’s new acquaintance holds a crossbow in the sporting-goods store.Source ↗
Dee’s diaryOnly recorded here so far
Charlie examines the illustrated diary he found in Dee’s old room.Source ↗
The bicep flyerOnly recorded here so far
Dennis’s prospective guest examines the oddly shaped paper invitation.Source ↗
Costumes
Bathrobes10 other recorded episodes
Dee and Frank wear bathrobes during Bruce’s supposed relationship exercise.Source ↗
Frank’s wig6 other recorded episodes
Frank’s Seamus disguise includes an attached ponytail.Source ↗
Wedding dresses5 other recorded episodes
Dee wears a white bridal dress and veil.Source ↗
FOLLOW THE THREAD
CONNECTED EPISODES.
S02 E04 
Connected through The party mansion, Frank’s wig, Bathrobes and 6 more.
S02 E10 Connected through Bruce Mathis, Paddy’s Pub, Frank Reynolds and 4 more.
S08 E03 Connected through Weddings, Wedding dresses, Paddy’s Pub and 5 more.
S09 E09 
Connected through Weddings, Wedding dresses, Paddy’s Pub and 5 more.
SOURCES & NOTES.
Tags document researched occurrences, not every appearance. Read the research notes and attribution.