ACROSS
 1. <flood> SPATE = SPAT _E
 4. <rock> VACILLATE = ←[-m]ETALLICA V←
 9. <replace> SUPERSEDE = PER S_ inside SUEDE
10. <blame> GUILT = GUI + LT
11. AIRS HIP = AIRSHIP <zeppelin>
12. PILL outside T_ F_ A = PITFALL <unexpected danger>
13. <farm> RANCH = RAN + C_ H_
15. "INCA WRECKED" = INCORRECT <false>
18. SING (LET ON) = SINGLETON <individual>
20. S + M inside A BA = SAMBA <dance>
22. <crack> ATTEMPT = A_T + TEMPT
24. ←I SEMEN← _S = NEMESIS <goddess>
26. A M BER[-k] = AMBER <gemstone>
27. <family origins> PARENTAGE = AREN'T inside PAGE
28. (SLAM METRO)* = MAELSTROM <chaos>
29. <detected odour of> SMELT <fish>

DOWN
 1. <tree> SASSAFRAS = SASS AS outside ←ARF←
 2. ASPIRING - G = ASPIRIN <painkiller>
 3. ⭯HEART⭯ = EARTH <terrain>
 4. VIE (TO WIN)* outside P + VIEWPOINT <stance>
 5. "CHEEP" = CHEAP <going for a song>
 6. (LARGE SUIT)* = LIGATURES <ties>
 7. <trouble> AGITATE = A GI TATE
 8. <praise> EXTOL = EX ←LOT←
14. "HAUL MARX" = HALLMARKS <distinctive features>
16. CON UND + RUM = CONUNDRUM <riddle>
17. <temporary> TRANSIENT = (INTERNS AT)*
19. <famed> NOTABLE = NOBLE outside TA
21. MA'S SAGE = MASSAGE <spa treatment>
22. (.c)ALAR M(u.) = ALARM <panic>
23. <ungulate> TAPIR = TAP + IR
25. <less> MINUS = MIN US