ACROSS
1. "JAM" = JAMB <part of doorway>
4. <intimidating> FEARSOME = F EARS O M E
9. BASTILLES* = BALLSIEST <most courageous>
10. (CUT IN)* = TUNIC <one shirty?>
12. <shininess> LUSTRE = LURE outside ST
13. <talk of bar> LEGALESE = LEE outside (G ALES)
15. (READ W) inside TATE + R = TREAD WATER <make no progress>
17. <board game> LUDO = LOUD, O→end
19. Y after OBE = OBEY <do as told>
20. DASH after BALDER = BALDERDASH <nonsense>
22. IMP UNITY = IMPUNITY <having no fear of consequences for bad behaviour>
23. <increased> HIGHER = "HIRE"
26. MICE outside N = MINCE <chopped meat>
27. <has a great time> LIVES IT UP = LIVE SITUP
28. PR A TALL outside F = PRATFALL <embarrassing blunder>
29. <nosedive> TANK <military vehicle>

DOWN
2. <book> ATLAS = AT LAS(-t)
3. <sit on> BESTRIDE = BEST RIDE
4. <show off guns> FLEX = "FLECKS"
5. (HYDRATE TEA)* = AT THE READY <prepared>
6. SAVANT* = SATNAV <travel guide>
7. <emperor> MONTEZUMA = MONTE "ZOOMER"
8. MOBILISATION* = ABOLITIONISM <anti-slavery cause>
11. (-tootha)CHE MOTHER A PY(-thon) = CHEMOTHERAPY <treatment>
14. <dance> TARANTELLA = TAR ANTE ←ALL←
16. OPENER after EYE = EYE-OPENER <shocking revelation>
18. <collection of toy vehicles> TRAIN SET = ←ART← + INSET
21. <depression> INDENT = TINNED*
24. <flirt with> HIT ON = HON outside IT
25. <cricket ground> OVAL = O(-n a) V(-ac)A(-nt) L(-ot)