This adventure was designed as a one-shot for a party of level 3 PCs relatively new to D&D 5e. It is a bait-and-switch social encounter that turns into combat, challenging players to improvise when their combat abilities are suboptimal. I used the nerfed vampire stat blocks included below but it can be scaled for other levels by adjusting those stats.
The social event of the season is the debutante ball for the Contessa of Understone! Lord Understone is a well-known social recluse, but he has opened his manor for this evening to introduce his daughter to well-heeled society. Invitations have been extended to eligible noble families throughout the county. This affords opportunities to adventurers as well: to mingle with the wealthy and powerful, make contacts, and of course pilferage…
Count Elric Understone Mature Vampire Armor Class 16 Hit Points 72 (retreat at ≤18 hp) Speed 30 ft. STR DEX CON INT WIS CHA 18 (+4) 16 (+3) 16 (+3) 12 (+1) 12 (+1) 14 (+2) Saving Throws Dex+8, Wis+6, Cha+7 Damage Resistances necrotic; slashing, piercing, or bludgeoning from nonmagical weapons unless silvered. Actions Multiattack May make two attacks per turn, only one of which can be a bite and only on a grappled or charmed target. Unarmed. Melee: +8 to hit, reach 5 ft., one target. Hit: 8 (1d8+4) piercing damage. Grapple. +8 vs target's Athletics or Acrobatics check, reach 5 ft., one target. Hit: target's Speed is reduced to 0 (Action to Athletics or Acrobatics vs Understone's +8 to escape). Bite. Melee: automatically hits grappled or charmed target. Hit: 7 (1d6+4) piercing damage. Charm. One humanoid target within 30 ft. will regard the caster as a friend and follow simple requests (Wisdom DC 13 save negates).
Mature Vampire
Armor Class 16
Hit Points 72 (retreat at ≤18 hp)
Speed 30 ft.
Saving Throws Dex+8, Wis+6, Cha+7
Damage Resistances necrotic; slashing, piercing, or bludgeoning from nonmagical weapons unless silvered.
Multiattack May make two attacks per turn, only one of which can be a bite and only on a grappled or charmed target.
Unarmed. Melee: +8 to hit, reach 5 ft., one target. Hit: 8 (1d8+4) piercing damage.
Grapple. +8 vs target's Athletics or Acrobatics check, reach 5 ft., one target. Hit: target's Speed is reduced to 0 (Action to Athletics or Acrobatics vs Understone's +8 to escape).
Bite. Melee: automatically hits grappled or charmed target. Hit: 7 (1d6+4) piercing damage.
Charm. One humanoid target within 30 ft. will regard the caster as a friend and follow simple requests (Wisdom DC 13 save negates).
Contessa Evelyn Understone Fledgling Vampire Armor Class 14 Hit Points 45 (retreat at ≤12 hp) Speed 30 ft. STR DEX CON INT WIS CHA 15 (+2) 14 (+2) 14 (+2) 12 (+1) 10 (+0) 14 (+2) Saving Throws Dex+5, Wis+3, Cha+5 Damage Resistances necrotic; slashing, piercing, or bludgeoning from nonmagical weapons unless silvered. Actions Multiattack May make two attacks per turn, only one of which can be a bite and only on a grabbed or charmed target. Unarmed. Melee: +6 to hit, reach 5 ft., one target. Hit: 6 (1d8+4) piercing damage. Grapple. +5 vs target's Athletics or Acrobatics check, reach 5 ft., one target. Hit: target's Speed is reduced to 0 (Action to Athletics or Acrobatics vs Contessa's +5 to escape). Bite. Melee: automatically hits grabbed or charmed target. Hit: 7 (1d6+4) piercing damage. Charm. One humanoid target within 30 ft. will regard the caster as a friend and follow simple requests (Wisdom DC 13 save negates).
Fledgling Vampire
Armor Class 14
Hit Points 45 (retreat at ≤12 hp)
Saving Throws Dex+5, Wis+3, Cha+5
Multiattack May make two attacks per turn, only one of which can be a bite and only on a grabbed or charmed target.
Unarmed. Melee: +6 to hit, reach 5 ft., one target. Hit: 6 (1d8+4) piercing damage.
Grapple. +5 vs target's Athletics or Acrobatics check, reach 5 ft., one target. Hit: target's Speed is reduced to 0 (Action to Athletics or Acrobatics vs Contessa's +5 to escape).
Bite. Melee: automatically hits grabbed or charmed target. Hit: 7 (1d6+4) piercing damage.
Servant Minions Variant Vampire Spawn Armor Class 12 Hit Points 1 Speed 30 ft. STR DEX CON INT WIS CHA 12 (+1) 12 (+1) 12 (+1) 10 (+0) 8 (-1) 13 (+1) Actions Unarmed. Melee: +4 to hit, reach 5 ft., one target. Hit: 5 (1d8+1) piercing damage. Grapple. +4 vs target's Athletics or Acrobatics check, reach 5 ft., one target. Hit: target's Speed is reduced to 0 (Action to Athletics or Acrobatics vs servant's +4 to escape).
Variant Vampire Spawn
Armor Class 12
Hit Points 1
Unarmed. Melee: +4 to hit, reach 5 ft., one target. Hit: 5 (1d8+1) piercing damage.
Grapple. +4 vs target's Athletics or Acrobatics check, reach 5 ft., one target. Hit: target's Speed is reduced to 0 (Action to Athletics or Acrobatics vs servant's +4 to escape).