Siren's Lure and Heidelberg Castle Timing Question

Is there a window between an action and the combat queued by Siren's Lure for a player to use Heidelberg Castle?

eg:
- vamp A attempts to block an action
- vamp B plays Siren's Lure
- action resolves

Does vamp A's controller have an opportunity at this point to use Heidelberg Castle?

Name: Siren's Lure
[BL:R1, LoB:R]
Cardtype: Action Modifier
Discipline: Melpominee/Celerity
[cel] This vampire burns 2 blood to get +1 stealth.
[mel] Only usable by an unlocked ready vampire other than the acting minion when a minion attempts to block. That minion cannot block this action. Lock this vampire and that minion. Once the action resolves, this vampire enters combat with that minion.
[MEL] As [mel] above, but do not lock this modifying vampire.
Artist: Steve Prescott

Name: Heidelberg Castle, Germany
[DS:U2, FN:PR, KMW:PAl, LoB:PI]
Cardtype: Master
Cost: 2 pool
Master: unique location.
Lock to move blood, equipment cards and/or retainers between any two ready vampires you control. (You choose the amount of blood you move and which cards you transfer.) Cannot be used during an action.
Artist: L. A. Williams

For that matter, is the combat created by Siren's Lure part of an action, or does it exist outside of any actions?